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The vector U bosons, or so-called “dark photons,” are one of the possible candidates for the dark matter mediators. They are supposed to interact with the standard matter via a “vector portal” due to the Uð1Þ − Uð1Þ0 symmetry group mixing which might make them visible in particle and heavy-ion experiments. While there is no confirmed observation of dark photons, the detailed analysis of different experimental data allows to estimate the upper limit for the kinetic mixing parameter ϵ2 depending on the mass MU of U bosons which is also unknown. In this study we present theoretical constraints on the upper limit of ϵ2ðMUÞ in the mass range MU ≤ 0.6 GeV from the comparison of the calculated dilepton spectra with the experimental data from the HADES collaboration at SIS18 energies where the dark photons are not observed. Our analysis is based on the microscopic Parton-Hadron-String Dynamics (PHSD) transport
approach which reproduces well the measured dilepton spectra in p þ p, p þ A and A þ A collisions. Additionally to the different dilepton channels originating from interactions and decays of ordinary matter particles (mesons and baryons), we incorporate the decay of hypothetical U bosons to dileptons, U → eþe−, where the U bosons themselves are produced by the Dalitz decay of pions π0 → γU, η mesons η → γU and Delta resonances Δ → NU. Our analysis can help to estimate the requested accuracy for future experimental searches of “light” dark photons by dilepton experiments.
Hypermassive hybrid stars (HMHS) are extreme astrophysical objects that could be produced in the merger of a binary system of compact stars. In contrast to their purely hadronic counterparts, hypermassive neutron stars (HMNS), these highly differentially rotating objects contain deconfined strange quark matter in their slowly rotating inner region. HMHS and HMNS are both mestastable configurations and can survive only shortly after the merger before collapsing to rotating black holes. The appearance of the phase transition from hadronic to quark matter in the interior region of the HMHS and its conjunction with the emitted GW will be addressed in this article by focussing on a specific case study of the delayed phase-transition scenario that takes place during the post-merger evolution of the remnant. The complicated dynamics of the collapse from the HMNS to the more compact HMHS will be analysed in detail. In particular, we will show that the interplay between the spatial density/temperature distributions and the rotational profiles in the interior of the wobbling HMHS after the collapse generates a high-temperature shell within the hadron-quark mixed phase region of the remnant.
Quasi-universal behavior of the threshold mass in unequal-mass, spinning binary neutron star mergers
(2021)
The lifetime of the remnant produced by the merger of two neutron stars can provide a wealth of information on the equation of state of nuclear matter and on the processes leading to the electromagnetic counterpart. Hence, it is essential to determine when this lifetime is the shortest, corresponding to when the remnant has a mass equal to the threshold mass, Mth, to prompt collapse to a black hole. We report on the results of more than 360 simulations of merging neutron-star binaries covering 40 different configurations differing in mass ratio and spin of the primary. Using this data, we have derived a quasi-universal relation for Mth and expressed its dependence on the mass ratio and spin of the binary. The new expression recovers the results of Koeppel et al. for equal-mass, irrotational binaries and reveals that Mth can increase (decrease) by 5% (10%) for binaries that have spins aligned (antialigned) with the orbital angular momentum and provides evidence for a nonmonotonic dependence of Mth on the mass asymmetry in the system. Finally, we extend to unequal masses and spinning binaries the lower limits that can be set on the stellar radii once a neutron star binary is detected, illustrating how the merger of an unequal-mass, rapidly spinning binary can significantly constrain the allowed values of the stellar radii.
Neutron-induced cross sections of short-lived nuclei are highly relevant in many domains such as fundamental nuclear physics, astrophysics and applications in nuclear technology. In particular, these cross sections are essential for understanding the synthesis of elements via the s- and r stellar processes. However, the measurement of such cross sections with current techniques is very difficult or even impossible, because of the difficulties to produce and handle the necessary amounts of radioactive nuclei. Reaching the nuclei of interest is only possible by inverting the reaction kinematics with radioactive beams.
In this contribution we present a project for indirectly determining neutron cross sections via the surrogate-reaction method. This project is based on the measurement of transfer- or inelastic-scattering-induced decay probabilities in inverse kinematics at storage rings. The measured probabilities are then used to tune nuclear-reaction models that will provide much more accurate predictions of the desired neutron cross sections. We also discuss a very ambitious, long-term project to directly measure neutron cross sections in inverse kinematics. It consists in the combination of a radioactive beam facility, an ion storage ring and a spallation neutron source.
The SU(3) pure gauge theory exhibits a first-order thermal deconfinement transition due to spontaneous breaking of its global Z3 center symmetry. When heavy dynamical quarks are added, this symmetry is broken explicitly and the transition weakens with decreasing quark mass until it disappears at a critical point. We compute the critical hopping parameter and the associated pion mass for lattice QCD with Nf=2 degenerate standard Wilson fermions on Nτ∈{6,8,10} lattices, corresponding to lattice spacings a=0.12 fm, a=0.09 fm, a=0.07 fm, respectively. Significant cutoff effects are observed, with the first-order region growing as the lattice gets finer. While current lattices are still too coarse for a continuum extrapolation, we estimate mcπ≈4 GeV with a remaining systematic error of ∼20%. Our results allow us to assess the accuracy of the leading-order and next-to-leading-order hopping expanded fermion determinant used in the literature for various purposes. We also provide a detailed investigation of the statistics required for this type of calculation, which is useful for similar investigations of the chiral transition.
The physical processes behind the production of light nuclei in heavy ion collisions are unclear. The successful theoretical description of experimental yields by thermal models conflicts with the very small binding energies of the observed states, being fragile in such a hot and dense environment. Other available ideas are delayed production via coalescence, or a cooling of the system after the chemical freeze-out according to a Saha equation, or a ‘quench’ instead of a thermal freeze-out. A recently derived prescription of an (interacting) Hagedorn gas is applied to consolidate the above pictures. The tabulation of decay rates of Hagedorn states into light nuclei allows to calculate yields usually inaccessible due to very poor Monte Carlo statistics. Decay yields of stable hadrons and light nuclei are calculated. While the scale-free decays of Hagedorn states alone are not compatible with the experimental data, a thermalized hadron and Hagedorn state gas is able to describe the experimental data. Applying a cooling of the system according to a Saha-equation with conservation of nucleon and anti-nucleon numbers leads to (nearly) temperature independent yields, thus a production of the light nuclei at temperatures much lower than the chemical freeze-out temperature is compatible with experimental data and with the statistical hadronization model.
The relativistic treatment of spin is a fundamental subject which has an old history. In various physical contexts it is necessary to separate the relativistic total angular momentum into an orbital and spin contribution. However, such decomposition is affected by ambiguities since one can always redefine the orbital and spin part through the so-called pseudo-gauge transformations. We analyze this problem in detail by discussing the most common choices of energy-momentum and spin tensors with an emphasis on their physical implications, and study the spin vector which is a pseudo-gauge invariant operator. We review the angular momentum decomposition as a crucial ingredient for the formulation of relativistic spin hydrodynamics and quantum kinetic theory with a focus on relativistic nuclear collisions, where spin physics has recently attracted significant attention. Furthermore, we point out the connection between pseudo-gauge transformations and the different definitions of the relativistic center of inertia. Finally, we consider the Einstein–Cartan theory, an extension of conventional general relativity, which allows for a natural definition of the spin tensor.
We report a measurement of the observed cross sections of e+ e− → J/ψX based on 3.21 fb − 1 of data accumulated at energies from 3.645 to 3.891 GeV with the BESIII detector operated at the BEPCII collider. In analysis of the cross sections, we measured the decay branching fractions of B(ψ(3686) → J/ψX) = (64.4 ± 0.6 ± 1.6)% and B(ψ(3770) → J/ψX) = (0.5 ± 0.2 ± 0.1)% for the first time. The energy-dependent line shape of these cross sections cannot be well described by two Breit-Wigner (BW) amplitudes of the expected decays ψ (3686) → J/ψX and ψ(3770) → J/ψX. Instead, it can be better described with one more BW amplitude of the decay R(3760)→ J/ψX. Under this assumption, we extracted the R (3760) mass M R (3760 ) = 3766.2 ± 3.8 ± 0.4 MeV/c2, total width Γ tot R ( 3760 ) = 22.2 ± 5.9 ± 1.4 MeV, and product of leptonic width and decay branching fraction
ΓeeR(3760) B[R(3760) → J/ψX] = (79.4 ± 85.5 ± 11.7) eV. The significance of the R(3760) is 5.3σ. The first uncertainties of these measured quantities are from fits to the cross sections and second systematic.
By analyzing 6.32 fb − 1 of e+ e− annihilation data collected at the center-of-mass energies between 4.178 and 4.226 GeV with the BESIII detector, we determine the branching fraction of the leptonic decay D + s → τ + ντ, with τ+ → π + π0¯ντ, to be B D + s → τ + ν τ = (5.29 ± 0.25 stat ± 0.20 syst) %. We estimate the product of the Cabibbo-Kobayashi-Maskawa matrix element |Vcs|and the D + s decay constant f D + s to be f D + s|Vcs| = (244.8 ± 5.8 stat ± 4.8syst) MeV, using the known values of the τ + and D + s masses as well as the D + s lifetime, together with our branching fraction measurement. Combining the value of |Vcs| obtained from a global fit in the standard model and f D + s from lattice quantum chromodynamics, we obtain f D + s = (251.6 ± 5.9 stat ± 4.9syst) MeV and |Vcs| = 0.980 ± 0.023 stat ± 0.019 syst. Using the branching fraction of B D + s → μ + νμ = (5.35±0.21)×10−3, we obtain the ratio of the branching fractions B D + s → τ + ντ/B D +s → μ+νμ = 9.89±0.71, which is consistent with the standard model prediction of lepton flavor universality.
The physics goal of the strong interaction program of the NA61/SHINE experiment at the CERN Super Proton Synchrotron (SPS) is to study the phase diagram of hadronic matter by a scan of particle production in collisions of nuclei with various sizes at a set of energies covering the SPS energy range. This paper presents differential inclusive spectra of transverse momentum, transverse mass and rapidity of π− mesons produced in central 40Ar+45Sc collisions at beam momenta of 13A, 19A, 30A, 40A, 75A and 150A Ge V /c. Energy and system size dependence of parameters of these distributions – mean transverse mass, the inverse slope parameter of transverse mass spectra, width of the rapidity distribution and mean multiplicity – are presented and discussed. Furthermore, the dependence of the ratio of the mean number of produced pions to the mean number of wounded nucleons on the collision energy was derived. The results are compared to predictions of several models.
The inclusive production of the J/ψ and ψ(2S) charmonium states is studied as a function of centrality in p-Pb collisions at a centre-of-mass energy per nucleon pair sNN−−−√ = 8.16 TeV at the LHC. The measurement is performed in the dimuon decay channel with the ALICE apparatus in the centre-of-mass rapidity intervals −4.46 < ycms < −2.96 (Pb-going direction) and 2.03 < ycms < 3.53 (p-going direction), down to zero transverse momentum (pT). The J/ψ and ψ(2S) production cross sections are evaluated as a function of the collision centrality, estimated through the energy deposited in the zero degree calorimeter located in the Pb-going direction. The pT-differential J/ψ production cross section is measured at backward and forward rapidity for several centrality classes, together with the corresponding average 〈pT〉 and ⟨p2T⟩ values. The nuclear effects affecting the production of both charmonium states are studied using the nuclear modification factor. In the p-going direction, a suppression of the production of both charmonium states is observed, which seems to increase from peripheral to central collisions. In the Pb-going direction, however, the centrality dependence is different for the two states: the nuclear modification factor of the J/ψ increases from below unity in peripheral collisions to above unity in central collisions, while for the ψ(2S) it stays below or consistent with unity for all centralities with no significant centrality dependence. The results are compared with measurements in p-Pb collisions at sNN−−−√ = 5.02 TeV and no significant dependence on the energy of the collision is observed. Finally, the results are compared with theoretical models implementing various nuclear matter effects.
The pT-differential production cross sections of prompt and non-prompt (produced in beauty-hadron decays) D mesons were measured by the ALICE experiment at midrapidity (|y| < 0.5) in proton-proton collisions at s√ = 5.02 TeV. The data sample used in the analysis corresponds to an integrated luminosity of (19.3 ± 0.4) nb−1. D mesons were reconstructed from their decays D0 → K−π+, D+ → K−π+π+, and D+s→φπ+→K−K+π+ and their charge conjugates. Compared to previous measurements in the same rapidity region, the cross sections of prompt D+ and D+s mesons have an extended pT coverage and total uncertainties reduced by a factor ranging from 1.05 to 1.6, depending on pT, allowing for a more precise determination of their pT-integrated cross sections. The results are well described by perturbative QCD calculations. The fragmentation fraction of heavy quarks to strange mesons divided by the one to non-strange mesons, fs/(fu + fd), is compatible for charm and beauty quarks and with previous measurements at different centre-of-mass energies and collision systems. The bb¯¯¯ production cross section per rapidity unit at midrapidity, estimated from non-prompt D-meson measurements, is dσbb¯¯¯/dy∣∣|y|<0.5=34.5±2.4(stat)+4.7−2.9(tot.syst) μb. It is compatible with previous measurements at the same centre-of-mass energy and with the cross section pre- dicted by perturbative QCD calculations.
The nature of the QCD chiral phase transition in the limit of vanishing quark masses has remained elusive for a long time, since it cannot be simulated directly on the lattice and is strongly cutoff-dependent. We report on a comprehensive ongoing study using unimproved staggered fermions with Nf ∈ [2, 8] mass-degenerate flavours on Nτ ∈ {4, 6, 8} lattices, in which we locate the chiral critical surface separating regions with first-order transitions from crossover regions in the bare parameter space of the lattice theory. Employing the fact that it terminates in a tricritical line, this surface can be extrapolated to the chiral limit using tricritical scaling with known exponents. Knowing the order of the transitions in the lattice parameter space, conclusions for approaching the continuum chiral limit in the proper order can be drawn. While a narrow first-order region cannot be ruled out, we find initial evidence consistent with a second-order chiral transition in all massless theories with Nf ≤ 6, and possibly up to the onset of the conformal window at 9 ≲ N∗f ≲ 12. A reanalysis of already published O(a)-improved Nf = 3 Wilson data on Nτ ∈ [4, 12] is also consistent with tricritical scaling, and the associated change from first to second-order on the way to the continuum chiral limit. We discuss a modified Columbia plot and a phase diagram for many-flavour QCD that reflect these possible features.
Two-particle angular correlations are measured in high-multiplicity proton-proton collisions at s√ = 13 TeV by the ALICE Collaboration. The yields of particle pairs at short-(∆η ∼ 0) and long-range (1.6 < |∆η| < 1.8) in pseudorapidity are extracted on the near-side (∆φ ∼ 0). They are reported as a function of transverse momentum (pT) in the range 1 < pT < 4 GeV/c. Furthermore, the event-scale dependence is studied for the first time by requiring the presence of high-pT leading particles or jets for varying pT thresholds. The results demonstrate that the long-range “ridge” yield, possibly related to the collective behavior of the system, is present in events with high-pT processes as well. The magnitudes of the short- and long-range yields are found to grow with the event scale. The results are compared to EPOS LHC and PYTHIA 8 calculations, with and without string-shoving interactions. It is found that while both models describe the qualitative trends in the data, calculations from EPOS LHC show a better quantitative agreement for the pT dependency, while overestimating the event-scale dependency.
Jet fragmentation transverse momentum distributions in pp and p-Pb collisions at √s, √sNN = 5.02 TeV
(2021)
Jet fragmentation transverse momentum (jT) distributions are measured in proton-proton (pp) and proton-lead (p-Pb) collisions at sNN−−−√ = 5.02 TeV with the ALICE experiment at the LHC. Jets are reconstructed with the ALICE tracking detectors and electromagnetic calorimeter using the anti-kT algorithm with resolution parameter R = 0.4 in the pseudorapidity range |η| < 0.25. The jT values are calculated for charged particles inside a fixed cone with a radius R = 0.4 around the reconstructed jet axis. The measured jT distributions are compared with a variety of parton-shower models. Herwig and PYTHIA 8 based models describe the data well for the higher jT region, while they underestimate the lower jT region. The jT distributions are further characterised by fitting them with a function composed of an inverse gamma function for higher jT values (called the “wide component”), related to the perturbative component of the fragmentation process, and with a Gaussian for lower jT values (called the “narrow component”), predominantly connected to the hadronisation process. The width of the Gaussian has only a weak dependence on jet transverse momentum, while that of the inverse gamma function increases with increasing jet transverse momentum. For the narrow component, the measured trends are successfully described by all models except for Herwig. For the wide component, Herwig and PYTHIA 8 based models slightly underestimate the data for the higher jet transverse momentum region. These measurements set constraints on models of jet fragmentation and hadronisation.
The ALICE Collaboration reports the first fully-corrected measurements of the N-subjettiness observable for track-based jets in heavy-ion collisions. This study is performed using data recorded in pp and Pb-Pb collisions at centre-of-mass energies of s√ = 7 TeV and sNN−−−√ = 2.76 TeV, respectively. In particular the ratio of 2-subjettiness to 1-subjettiness, τ2/τ1, which is sensitive to the rate of two-pronged jet substructure, is presented. Energy loss of jets traversing the strongly interacting medium in heavy-ion collisions is expected to change the rate of two-pronged substructure relative to vacuum. The results are presented for jets with a resolution parameter of R = 0.4 and charged jet transverse momentum of 40 ≤ pT,jet ≤ 60 GeV/c, which constitute a larger jet resolution and lower jet transverse momentum interval than previous measurements in heavy-ion collisions. This has been achieved by utilising a semi-inclusive hadron-jet coincidence technique to suppress the larger jet combinatorial background in this kinematic region. No significant modification of the τ2/τ1 observable for track-based jets in Pb-Pb collisions is observed relative to vacuum PYTHIA6 and PYTHIA8 references at the same collision energy. The measurements of τ2/τ1, together with the splitting aperture angle ∆R, are also performed in pp collisions at s√ = 7 TeV for inclusive jets. These results are compared with PYTHIA calculations at s√ = 7 TeV, in order to validate the model as a vacuum reference for the Pb-Pb centre-of-mass energy. The PYTHIA references for τ2/τ1 are shifted to larger values compared to the measurement in pp collisions. This hints at a reduction in the rate of two-pronged jets in Pb-Pb collisions compared to pp collisions.
The transverse momentum (pT) differential cross section of the charm-strange baryon Ξ0c is measured at midrapidity (|y| < 0.5) via its semileptonic decay into e+Ξ−νe in pp collisions at s√ = 5.02 TeV with the ALICE detector at the LHC. The ratio of the pT-differential Ξ0c-baryon and D0-meson production cross sections is also reported. The measurements are compared with simulations with different tunes of the PYTHIA 8 event generator, with predictions from a statistical hadronisation model (SHM) with a largely augmented set of charm-baryon states beyond the current lists of the Particle Data Group, and with models including hadronisation via quark coalescence. The pT-integrated cross section of prompt Ξ0c-baryon production at midrapidity is also reported, which is used to calculate the baryon-to-meson ratio Ξ0c/D0 = 0.20 ± 0.04 (stat.)+0.08−0.07 (syst.). These results provide an additional indication of a modification of the charm fragmentation from e+e− and e−p collisions to pp collisions.
Measurements of elliptic (v2) and triangular (v3) flow coefficients of π±, K±, p+p¯¯¯, K0S, and Λ+Λ¯¯¯¯ obtained with the scalar product method in Xe-Xe collisions at sNN−−−√ = 5.44 TeV are presented. The results are obtained in the rapidity range |y| < 0.5 and reported as a function of transverse momentum, pT, for several collision centrality classes. The flow coefficients exhibit a particle mass dependence for pT < 3 GeV/c, while a grouping according to particle type (i.e., meson and baryon) is found at intermediate transverse momenta (3 < pT < 8 GeV/c). The magnitude of the baryon v2 is larger than that of mesons up to pT = 6 GeV/c. The centrality dependence of the shape evolution of the pT-differential v2 is studied for the various hadron species. The v2 coefficients of π±, K±, and p+p¯¯¯ are reproduced by MUSIC hydrodynamic calculations coupled to a hadronic cascade model (UrQMD) for pT < 1 GeV/c. A comparison with vn measurements in the corresponding centrality intervals in Pb-Pb collisions at sNN−−−√ = 5.02 TeV yields an enhanced v2 in central collisions and diminished value in semicentral collisions.
The electromagnetic process is studied with the initial-state-radiation technique using 7.5 fb−1 of data collected by the BESIII experiment at seven energy points from 3.773 to 4.600 GeV. The Born cross section and the effective form factor of the proton are measured from the production threshold to 3.0 GeV/ using the invariant-mass spectrum. The ratio of electric and magnetic form factors of the proton is determined from the analysis of the proton-helicity angular distribution.
We report on the inclusive J/ψ production cross section measured at the CERN Large Hadron Collider in proton–proton collisions at a center-of-mass energy s√ = 13 TeV. The J/ψ mesons are reconstructed in the e+e− decay channel and the measurements are performed at midrapidity (|y|<0.9) in the transverse-momentum interval 0<pT<40 GeV/c, using a minimum-bias data sample corresponding to an integrated luminosity Lint=32.2 nb−1 and an Electromagnetic Calorimeter triggered data sample with Lint=8.3 pb−1. The pT-integrated J/ψ production cross section at midrapidity, computed using the minimum-bias data sample, is dσ/dy|y=0=8.97±0.24 (stat)±0.48 (syst)±0.15 (lumi) μb. An approximate logarithmic dependence with the collision energy is suggested by these results and available world data, in agreement with model predictions. The integrated and pT-differential measurements are compared with measurements in pp collisions at lower energies and with several recent phenomenological calculations based on the non-relativistic QCD and Color Evaporation models.
Measurements of event-by-event fluctuations of charged-particle multiplicities in Pb–Pb collisions at sNN−−−√ = 2.76 TeV using the ALICE detector at the CERN Large Hadron Collider (LHC) are presented in the pseudorapidity range |η|<0.8 and transverse momentum 0.2<pT<2.0 GeV/c. The amplitude of the fluctuations is expressed in terms of the variance normalized by the mean of the multiplicity distribution. The η and pT dependences of the fluctuations and their evolution with respect to collision centrality are investigated. The multiplicity fluctuations tend to decrease from peripheral to central collisions. The results are compared to those obtained from HIJING and AMPT Monte Carlo event generators as well as to experimental data at lower collision energies. Additionally, the measured multiplicity fluctuations are discussed in the context of the isothermal compressibility of the high-density strongly-interacting system formed in central Pb–Pb collisions.
Two-particle Azimuthal correlations are measured with the ALICE apparatus in pp collisions at s√=13 TeV to explore strangeness- and multiplicity-related effects in the fragmentation of jets and the transition regime between bulk and hard production, probed with the condition that a strange meson (KS0) or baryon (Λ) with transverse momentum pT>3 GeV/c is produced. Azimuthal correlations between kaons or Λ hyperons with other hadrons are presented at midrapidity for a broad range of the trigger (3<ptriggT<20 GeV/c) and associated particle pT (1 GeV/c <passocT<ptriggT), for minimum-bias events and as a function of the event multiplicity. The near- and away-side peak yields are compared for the case of either KS0 or Λ(Λ¯¯¯¯) being the trigger particle with that of inclusive hadrons (a sample dominated by pions). In addition, the measurements are compared with predictions from PYTHIA 8 and EPOS LHC event generators.
The production of π±, K±, K0S, K∗(892)0, p, ϕ(1020), Λ, Ξ−, Ω−, and their antiparticles was measured in inelastic proton–proton (pp) collisions at a center-of-mass energy of s√ = 13 TeV at midrapidity (|y|<0.5) as a function of transverse momentum (pT) using the ALICE detector at the CERN LHC. Furthermore, the single-particle pT distributions of K0S, Λ, and Λ¯¯¯¯ in inelastic pp collisions at s√=7 TeV are reported here for the first time. The pT distributions are studied at midrapidity within the transverse momentum range 0≤pT≤20 GeV/c, depending on the particle species. The pT spectra, integrated yields, and particle yield ratios are discussed as a function of collision energy and compared with measurements at lower s√ and with results from various general-purpose QCD-inspired Monte Carlo models. A hardening of the spectra at high pT with increasing collision energy is observed, which is similar for all particle species under study. The transverse mass and xT≡2pT/s√ scaling properties of hadron production are also studied. As the collision energy increases from s√ = 7–13 TeV, the yields of non- and single-strange hadrons normalized to the pion yields remain approximately constant as a function of s√, while ratios for multi-strange hadrons indicate enhancements. The pT-differential cross sections of π±, K± and p (p¯¯¯) are compared with next-to-leading order perturbative QCD calculations, which are found to overestimate the cross sections for π± and p (p¯¯¯) at high pT.
The coherent photoproduction of J/ψ and ψ′ mesons was measured in ultra-peripheral Pb–Pb collisions at a center-of-mass energy sNN−−−√ = 5.02 TeV with the ALICE detector. Charmonia are detected in the central rapidity region for events where the hadronic interactions are strongly suppressed. The J/ψ is reconstructed using the dilepton (l+l−) and proton–antiproton decay channels, while for the ψ′ the dilepton and the l+l−π+π− decay channels are studied. The analysis is based on an event sample corresponding to an integrated luminosity of about 233 μb−1. The results are compared with theoretical models for coherent J/ψ and ψ′ photoproduction. The coherent cross section is found to be in a good agreement with models incorporating moderate nuclear gluon shadowing of about 0.64 at a Bjorken-x of around 6×10−4, such as the EPS09 parametrization, however none of the models is able to fully describe the rapidity dependence of the coherent J/ψ cross section including ALICE measurements at forward rapidity. The ratio of ψ′ to J/ψ coherent photoproduction cross sections was also measured and found to be consistent with the one for photoproduction off protons.
The production of ϕ mesons has been studied in pp collisions at LHC energies with the ALICE detector via the dimuon decay channel in the rapidity region 2.5<y<4. Measurements of the differential cross section d2σ/dydpT are presented as a function of the transverse momentum (pT) at the center-of-mass energies s√=5.02, 8 and 13 TeV and compared with the ALICE results at midrapidity. The differential cross sections at s√=5.02 and 13 TeV are also studied in several rapidity intervals as a function of pT, and as a function of rapidity in three pT intervals. A hardening of the pT-differential cross section with the collision energy is observed, while, for a given energy, pT spectra soften with increasing rapidity and, conversely, rapidity distributions get slightly narrower at increasing pT. The new results, complementing the published measurements at s√=2.76 and 7 TeV, allow one to establish the energy dependence of ϕ meson production and to compare the measured cross sections with phenomenological models. None of the considered models manages to describe the evolution of the cross section with pT and rapidity at all the energies.
Constraints on the Covariant Canonical Gauge Gravity (CCGG) theory from low-redshift cosmology are studied. The formulation extends Einstein’s theory of General Relativity (GR) by a quadratic Riemann–Cartan term in the Lagrangian, controlled by a “deformation” parameter. In the Friedman universe this leads to an additional geometrical stress energy and promotes, due to the necessary presence of torsion, the cosmological constant to a time-dependent function. The MCMC analysis of the combined data sets of Type Ia Supernovae, Cosmic Chronometers and Baryon Acoustic Oscillations yields a fit that is well comparable with the ΛCDM results. The modifications implied in the CCGG approach turn out to be subdominant in the low-redshift cosmology. However, a non-zero spatial curvature and deformation parameter are shown to be consistent with observations.
The first measurements of the production of muons and electrons from heavy-flavour hadron decays in Xe–Xe collisions at √sNN = 5.44 TeV, using the ALICE detector at the LHC, are reported. The measurement of the nuclear modification factor RAA is performed as a function of transverse momentum pT in several centrality classes at forward rapidity (2.5 < y < 4) and midrapidity (|y| < 0.8) for muons and electrons from heavy-flavour hadron decays, respectively. A suppression by a factor up to about 2.5 compared to the binary-scaled pp reference is observed in central collisions at both central and forward rapidities. The RAA of muons from heavy-flavour hadron decays is compared to previous measurements in Pb–Pb collisions at √sNN = 5.02 TeV. When the nuclear modification factors are compared in the centrality classes 0–10% for Xe–Xe collisions and 10–20% for Pb–Pb collisions, which have similar charged-particle multiplicity density, a similar suppression, with RAA ∼ 0.4 in the pT interval 4 < pT < 8 GeV/c, is observed. The comparison of the measured RAA values in the two collision systems brings new insights on the properties of the quark-gluon plasma by investigating the system-size and geometry dependence of medium-induced parton energy loss. The results of muons and electrons from heavy-flavour hadron decays provide new constraints to model calculations.
Measurements of the production of muons from heavy-flavour hadron decays in Pb–Pb collisions at √sNN = 5.02 and 2.76 TeV using the ALICE detector at the LHC are reported. The nuclear modification factor RAA at √sNN = 5.02 TeV is measured at forward rapidity (2.5 < y < 4) as a function of transverse momentum pT in central, semi-central, and peripheral collisions over a wide pT interval, 3 < pT < 20 GeV/c, in which muons from beauty-hadron decays are expected to take over from charm as the dominant source at high pT (pT > 7 GeV/c). The RAA shows an increase of the suppression of the yields of muons from heavy-flavour hadron decays with increasing centrality. A suppression by a factor of about three is observed in the 10% most central collisions. The RAA at √sNN = 5.02 TeV is similar to that at √sNN = 2.76 TeV. The precise RAA measurements have the potential to distinguish between model predictions implementing different mechanisms of parton energy loss in the high-density medium formed in heavy-ion collisions. They place important constraints for the understanding of the heavy-quark interaction with the hot and dense QCD medium.
The HADES experiment at GSI has recently provided data on the flow coefficients v1,..., v4 for protons in Au+Au reactions at Elab = 1.23 AGeV (or √sNN = 2.4 GeV). This data allows to estimate the shear viscosity over entropy density ratio, η/s at low energies via a coarse graining analysis of the UrQMD transport simulations of the flow harmonics in comparison to the experimental data. By this we can provide for the first time an estimate of η/s ≈ 0.65 ± 0.15 (or (8 ± 2)(4π)−1) at such low energies.
ϒ production and nuclear modification at forward rapidity in Pb–Pb collisions at √sNN = 5.02TeV
(2021)
The production of ϒ mesons in Pb–Pb collisions at a centre-of-mass energy per nucleon pair √sNN = 5.02 TeV is measured with the muon spectrometer of the ALICE detector at the LHC. The yields as well as the nuclear modification factors are determined in the forward rapidity region 2.5 < y < 4.0, as a function of rapidity, transverse momentum and collision centrality. The results show that the production of the ϒ(1S) meson is suppressed by a factor of about three with respect to the production in proton–proton collisions. For the first time, a significant signal for the ϒ(2S) meson is observed at forward rapidity, indicating a suppression stronger by about a factor 2–3 with respect to the ground state. The measurements are compared with transport, hydrodynamic, comover and statistical hadronisation model calculations.
The first measurement of the coherent photoproduction of ρ0 vector mesons in ultra-peripheral Xe–Xe collisions at √sNN = 5.44 TeV is presented. This result, together with previous HERA γ p data and γ –Pb measurements from ALICE, describes the atomic number (A) dependence of this process, which is particularly sensitive to nuclear shadowing effects and to the approach to the black-disc limit of QCD at a semi-hard scale. The cross section of the Xe + Xe → ρ0 + Xe + Xe process, measured at midrapidity through the decay channel ρ0 → π+π−, is found to be dσ/dy = 131.5 ± 5.6(stat.)+17.5 −16.9(syst.) mb. The ratio of the continuum to resonant contributions for the production of pion pairs is also measured. In addition, the fraction of events accompanied by electromagnetic dissociation of either one or both colliding nuclei is reported. The dependence on A of cross section for the coherent ρ0 photoproduction at a centre-of-mass energy per nucleon of the γ A system of Wγ A,n = 65 GeV is found to be consistent with a power-law behaviour σ(γ A → ρ0 A) ∝ Aα with a slope α = 0.96 ± 0.02(syst.). This slope signals important shadowing effects, but it is still far from the behaviour expected in the black-disc limit.
The first measurement of the cross section for coherent J/ψ photoproduction as a function of |t|, the square of the momentum transferred between the incoming and outgoing target nucleus, is presented. The data were measured with the ALICE detector in ultra-peripheral Pb–Pb collisions at a centre-of-mass energy per nucleon pair √sNN = 5.02 TeV with the J/ψ produced in the central rapidity region |y| < 0.8,
which corresponds to the small Bjorken-x range (0.3 − 1.4) × 10−3.
The measured |t|-dependence is not described by computations based only on the Pb nuclear form factor, while the photonuclear cross section is better reproduced by models including shadowing according to the leading-twist approximation, or gluon-saturation effects from the impact-parameter dependent Balitsky–Kovchegov equation. These new results are therefore a valid tool to constrain the relevant model parameters and to investigate the transverse gluonic structure at very low Bjorken-x.
The polarization of inclusive J/ψ and ϒ(1S) produced in Pb–Pb collisions at √sNN = 5.02 TeV at the LHC is measured with the ALICE detector. The study is carried out by reconstructing the quarkonium through its decay to muon pairs in the rapidity region 2.5 < y < 4 and measuring the polar and azimuthal angular distributions of the muons. The polarization parameters λθ , λφ and λθφ are measured in the helicity and Collins-Soper reference frames, in the transverse momentum interval 2 < pT < 10 GeV/c and pT < 15 GeV/c for the J/ψ and ϒ(1S), respectively. The polarization parameters for the J/ψ are found to be compatible with zero, within a maximum of about two standard deviations at low pT, for both reference frames and over the whole pT range. The values are compared with the corresponding results obtained for pp collisions at √s = 7 and 8 TeV in a similar kinematic region by the ALICE and LHCb experiments. Although with much larger uncertainties, the polarization parameters for ϒ(1S) production in Pb–Pb collisions are also consistent with zero.
Deuteron production in high-energy collisions is sensitive to the space–time evolution of the collision system, and is typically described by a coalescence mechanism. For the first time, we present results on jet-associated deuteron production in pp collisions at √s = 13 TeV, providing an opportunity to test the established picture for deuteron production in events with a hard scattering. Using a trigger particle with high transverse-momentum (pT > 5 GeV/c) as a proxy for the presence of a jet at midrapidity, we observe a measurable population of deuterons being produced around the jet proxy. The associated deuteron yield measured in a narrow angular range around the trigger particle differs by 2.4–4.8 standard deviations from the uncorrelated background. The data are described by PYTHIA model calculations featuring baryon coalescence.
Pion-kaon femtoscopy and the lifetime of the hadronic phase in Pb-Pb collisions at √sNN = 2.76 TeV
(2021)
In this paper, the first femtoscopic analysis of pion–kaon correlations at the LHC is reported. The analysis was performed on the Pb–Pb collision data at √sNN = 2.76 TeV recorded with the ALICE detector. The non-identical particle correlations probe the spatio-temporal separation between sources of different particle species as well as the average source size of the emitting system. The sizes of the pion and kaon sources increase with centrality, and pions are emitted closer to the centre of the system and/or later than kaons. This is naturally expected in a system with strong radial flow and is qualitatively reproduced by hydrodynamic models. ALICE data on pion–kaon emission asymmetry are consistent with (3+1)-dimensional viscous hydrodynamics coupled to a statistical hadronisation model, resonance propagation, and decay code THERMINATOR 2 calculation, with an additional time delay between 1 and 2 fm/c for kaons. The delay can be interpreted as evidence for a significant hadronic rescattering phase in heavy-ion collisions at the LHC.
The Time Projection Chamber (TPC) of the ALICE experiment at the CERN LHC was upgraded for Run 3 and Run 4. Readout chambers based on Gas Electron Multiplier (GEM) technology and a new readout scheme allow continuous data taking at the highest interaction rates expected in Pb-Pb collisions. Due to the absence of a gating grid system, a significant amount of ions created in the multiplication region is expected to enter the TPC drift volume and distort the uniform electric field that guides the electrons to the readout pads. Analytical calculations were considered to correct for space-charge distortion fluctuations but they proved to be too slow for the calibration and reconstruction workflow in Run 3. In this paper, we discuss a novel strategy developed by the ALICE Collaboration to perform distortion-fluctuation corrections with machine learning and convolutional neural network techniques. The results of preliminary studies are shown and the prospects for further development and optimization are also discussed.
It is shown that the inclusion of hadronic interactions, and in particular nuclear potentials, in simulations of heavy ion collisions at the SPS energy range can lead to obvious correlations of protons. These correlations contribute significantly to an intermittency analysis as performed at the NA61 experiment. The beam energy and system size dependence is studied by comparing the resulting intermittency index for heavy ion collisions of different nuclei at beam energies of 40A, 80A and 150A GeV. The resulting intermittency index from our simulations is similar to the reported values of the NA61 collaboration, if nuclear interactions are included. The observed apparent intermittency signal is the result of the correlated proton pairs with small relative transverse momentum Δpt, which would be enhanced by hadronic potentials, and this correlation between the protons is slightly influenced by the coalescence parameters and the relative invariant four-momentum qinv cut.
The thermal fit to preliminary HADES data of Au+Au collisions at sNN=2.4 GeV shows two degenerate solutions at T≈50 MeV and T≈70 MeV. The analysis of the same particle yields in a transport simulation of the UrQMD model yields the same features, i.e. two distinct temperatures for the chemical freeze-out. While both solutions yield the same number of hadrons after resonance decays, the feeddown contribution is very different for both cases. This highlights that two systems with different chemical composition can yield the same multiplicities after resonance decays. The nature of these two minima is further investigated by studying the time-dependent particle yields and extracted thermodynamic properties of the UrQMD model. It is confirmed, that the evolution of the high temperature solution resembles cooling and expansion of a hot and dense fireball. The low temperature solution displays an unphysical evolution: heating and compression of matter with a decrease of entropy. These results imply that the thermal model analysis of systems produced in low energy nuclear collisions is ambiguous but can be interpreted by taking also the time evolution and resonance contributions into account.
Using data samples collected with the BESIII detector operating at the BEPCII storage ring at center-of-mass energies from 4.178 to 4.600 GeV, we study the process eþe− → π0Xð3872Þγ and search for Zcð4020Þ0 → Xð3872Þγ. We find no significant signal and set upper limits on σðeþe− → π0Xð3872ÞγÞ · BðXð3872Þ → πþπ−J=ψÞ and σðeþe− → π0Zcð4020Þ0Þ · BðZcð4020Þ0 → Xð3872ÞγÞ · BðXð3872Þ → πþπ−J=ψÞ for each energy point at 90% confidence level, which is of the order of several tenths pb.
We measure the inclusive semielectronic decay branching fraction of the D+s meson. A double-tag technique is applied to e+e− annihilation data collected by the BESIII experiment at the BEPCII collider, operating in the center-of-mass energy range 4.178–4.230 GeV. We select positrons fromD+s→Xe+νe with momenta greater than 200 MeV/c and determine the laboratory momentum spectrum, accounting for the effects of detector efficiency and resolution. The total positron yield and semielectronic branching fraction are determined by extrapolating this spectrum below the momentum cutoff. We measure the D+s semielectronic branching fraction to be(6.30±0.13(stat.)±0.09(syst.)±0.04(ext.))%, showing no evidence for unobserved exclusive semielectronic modes. We combine this result with external data taken from literature to determine the ratio of the D+s and D0 semielectronic widths, Γ(D+s→Xe+νe)Γ(D0→Xe+νe)=0.790±0.016(stat.)±0.011(syst.)±0.016(ext.). Our results are consistent with and more precise than previous measurements.
Correlations between moments of different flow coefficients are measured in Pb–Pb collisions at √sNN=5.02TeV recorded with the ALICE detector. These new measurements are based on multiparticle mixed harmonic cumulants calculated using charged particles in the pseudorapidity region |η| <0.8with the transverse momentum range 0.2 <pT<5.0GeV/c. The centrality dependence of correlations between two flow coefficients as well as the correlations between three flow coefficients, both in terms of their second moments, are shown. In addition, a collection of mixed harmonic cumulants involving higher moments of v2and v3is measured for the first time, where the characteristic signature of negative, positive and negative signs of four-, six-and eight-particle cumulants are observed, respectively. The measurements are compared to the hydrodynamic calculations using iEBE-VISHNU with AMPT and TRENTo initial conditions. It is shown that the measurements carried out using the LHC Run 2 data in 2015 have the precision to explore the details of initial-state fluctuations and probe the nonlinear hydrodynamic response of v2and v3to their corresponding initial anisotropy coefficients ε2and ε3. These new studies on correlations between three flow coefficients as well as correlations between higher moments of two different flow coefficients will pave the way to tighten constraints on initial-state models and help to extract precise information on the dynamic evolution of the hot and dense matter created in heavy-ion collisions at the LHC.
When a very strong light field is applied to a molecule an electron can be ejected by tunneling. In order to quantify the time-resolved dynamics of this ionization process, the concept of the Wigner time delay can be used. The properties of this process can depend on the tunneling direction relative to the molecular axis. Here, we show experimental and theoretical data on the Wigner time delay for tunnel ionization of H2 molecules and demonstrate its dependence on the emission direction of the electron with respect to the molecular axis. We find, that the observed changes in the Wigner time delay can be quantitatively explained by elongated/shortened travel paths of the emitted electrons, which occur due to spatial shifts of the electrons’ birth positions after tunneling. Our work provides therefore an intuitive perspective towards the Wigner time delay in strong-field ionization.
Production of pions, kaons, (anti-)protons and φ mesons in Xe–Xe collisions at √sNN = 5.44 TeV
(2021)
The first measurement of the production of pions, kaons, (anti-)protons and φ mesons at midrapidity in Xe–Xe collisions at √sNN = 5.44 TeV is presented. Transverse momentum (pT) spectra and pT-integrated yields are extracted in several centrality intervals bridging from p–Pb to mid-central Pb–Pb collisions in terms of final-state multiplicity. The study of Xe–Xe and Pb–Pb collisions allows systems at similar charged-particle multiplicities but with different initial geometrical eccentricities to be investigated. A detailed comparison of the spectral shapes in the two systems reveals an opposite behaviour for radial and elliptic flow. In particular, this study shows that the radial flow does not depend on the colliding system when compared at similar charged-particle multiplicity. In terms of hadron chemistry, the previously observed smooth evolution of particle ratios with multiplicity from small to large collision systems is also found to hold in Xe–Xe. In addition, our results confirm that two remarkable features of particle production at LHC energies are also valid in the collision of medium-sized nuclei: the lower proton-to-pion ratio with respect to the thermal model expectations and the increase of the φ-to-pion ratio with increasing final-state multiplicity.
Themultiplicity dependence of the pseudorapidity density of charged particles in proton–proton (pp) collisions at centre-of-mass energies √s = 5.02, 7 and 13 TeV measured by ALICE is reported. The analysis relies on track segments measured in the midrapidity range (|η| < 1.5). Results are presented for inelastic events having at least one charged particle produced in the pseudorapidity interval |η| < 1. The multiplicity dependence of the pseudorapidity density of charged particles is measured with mid- and forward rapidity multiplicity estimators, the latter being less affected by autocorrelations.Adetailed comparison with predictions from the PYTHIA 8 and EPOS LHC event generators is also presented. The results can be used to constrain models for particle production as a function of multiplicity in pp collisions.
The absolute-scale electronic energetics of liquid water and aqueous solutions, both in the bulk and at associated interfaces, are the central determiners of water-based chemistry. However, such information is generally experimentally inaccessible. Here we demonstrate that a refined implementation of the liquid microjet photoelectron spectroscopy (PES) technique can be adopted to address this. Implementing concepts from condensed matter physics, we establish novel all-liquid-phase vacuum and equilibrated solution–metal-electrode Fermi level referencing procedures. This enables the precise and accurate determination of previously elusive water solvent and solute vertical ionization energies, VIEs. Notably, this includes quantification of solute-induced perturbations of water's electronic energetics and VIE definition on an absolute and universal chemical potential scale. Defining and applying these procedures over a broad range of ionization energies, we accurately and respectively determine the VIE and oxidative stability of liquid water as 11.33 ± 0.03 eV and 6.60 ± 0.08 eV with respect to its liquid-vacuum-interface potential and Fermi level. Combining our referencing schemes, we accurately determine the work function of liquid water as 4.73 ± 0.09 eV. Further, applying our novel approach to a pair of exemplary aqueous solutions, we extract absolute VIEs of aqueous iodide anions, reaffirm the robustness of liquid water's electronic structure to high bulk salt concentrations (2 M sodium iodide), and quantify reference-level dependent reductions of water's VIE and a 0.48 ± 0.13 eV contraction of the solution's work function upon partial hydration of a known surfactant (25 mM tetrabutylammonium iodide). Our combined experimental accomplishments mark a major advance in our ability to quantify electronic–structure interactions and chemical reactivity in liquid water, which now explicitly extends to the measurement of absolute-scale bulk and interfacial solution energetics, including those of relevance to aqueous electrochemical processes.
Classical light microscopy is one of the main tools for science to study small things. Microscopes and their technology and optics have been developed and improved over centuries, however their resolution is ultimately restricted physically by the diffraction of light based on its wave nature described by Maxwell’s equations. Hence, the nanoworld – often characterized by sub-100-nm structural sizes – is not accessible with classical far-field optics (apart from special x-ray laser concepts) since its lateral resolution scales with the wavelength.
It was not until the 20th century that various technologies emerged to circumvent the diffraction limit, including so-called near-field microscopy. Although conceptually based on Maxwell’s long known equations, it took a long time for the scientific community to recognize its powerful opportunities and the first embodiments of near-field microscopes were developed. One representative of them is the scattering-type Scanning Near-field Optical Microscope (s-SNOM). It is a Scanning Probe Microscope (SPM) that enables imaging and spectroscopy at visible light frequencies down to even radio waves with a sub-100-nm resolution regardless of the wavelength used. This work also reflects this wide spectral range as it contains applications from near-infrared light down to deep THz/GHz radiation.
This thesis is subdivided into two parts. First, new experimental capabilities for the s-SNOM are demonstrated and evaluated in a more technical manner. Second, among other things, these capabilities are used to study various transport phenomena in solids, as already indicated in the title.
On the technical side, preliminary studies on the suitability of the qPlus sensor – a novel scanning probe technology – for near-field microscopy are presented.
The scanning head incorporating the qPlus sensor–named TRIBUS – is originally intended and built for ultra-high vacuum, low temperature, and high resolution applications. These are desirable environments and properties for sensitive nearfield measurements as well. However, since its design was not planned for near-field measurements, several special technical and optical aspects have to be taken into account, among others the scanning tip design and a spring suspended measurement head.
In addition, in this thesis field-effect transistors are used as THz detectors in an s-SNOM for the first time. Although THz s-SNOM is already an emerging technology, it still suffers from the requirements of sophisticated and specialized infrastructure on both the detector and laser side. Field-effect transistors offer an alternative that is flexible, cost-efficient, room-temperature operating, and easy to handle. Here, their suitability for s-SNOM measurements, which in general require very sensitive and fast detectors, is evaluated.
In the scientific part of this thesis, electromagnetic surface waves on silver nanowires and the conductivity/charge carrier density in silicon are investigated. Both are completely different concepts of transport phenomena, but this already shows the general versatility of the s-SNOM as it can enter both fields. Silver nanowires are analysed by means of near-infrared radiation. Their plasmonic behaviour in this spectral region is studied complementing other simulations and studies in literature performed on them using for example far-field optics.
Furthermore, the surface wave imaging ability of the s-SNOM in the near-infrared regime is thoroughly investigated in this thesis. Mapping surface waves in the mid-infrared regime is widespread in the community, however for much smaller wavelengths there are several important aspects to be considered additionally, such as the smaller focal spot size.
After that, doped and photo-excited silicon substrates are investigated. As the characteristic frequencies of charge carriers in semiconductors – described by the plasma frequency and the Drude model – are within the THz range, the THz s-SNOM is very well suited to probe their behaviour and to reveal contrasts, which has already been shown qualitatively by numerous literature reports. Here, the photo-excitation enables to set and tune the charge carrier density continuously.
Furthermore, the analysis of all silicon samples focuses on a quantitative extraction of the charge carrier densities and doping levels ...
We investigate general properties of the eigenvalue spectrum for improved staggered quarks. We introduce a new chirality operator [y5⊗1] and a new shift operator [1⊗ξ5], which respect the same recursion relation as the γ5 operator in the continuum. Then we show that matrix elements of the chirality operator sandwiched between two eigenstates of the staggered Dirac operator are related to those of the shift operator by the Ward identity of the conserved U (1)A symmetry of staggered fermion actions. We perform a numerical study in quenched QCD using HYP staggered quarks to demonstrate the Ward identity. We introduce a new concept of leakage patterns which collectively represent the matrix elements of the chirality operator and the shift operator sandwiched between two eigenstates of the staggered Dirac operator. The leakage pattern provides a new method to identify zero modes and nonzero modes in the Dirac eigenvalue spectrum. This method is as robust as the spectral flow method but requires much less computing power. Analysis using a machine learning technique confirms that the leakage pattern is universal, since the staggered Dirac eigenmodes on normal gauge configurations respect it. In addition, the leakage pattern can be used to determine a ratio of renormalization factors as a by-product. We conclude that it might be possible and realistic to measure the topological charge Q using the Atiya-Singer index theorem and the leakage pattern of the chirality operator in the staggered fermion formalism.
We derive the collision term in the Boltzmann equation using the equation of motion for the Wigner function of massive spin-1/2 particles. To next-to-lowest order in h, it contains a nonlocal contribution, which is responsible for the conversion of orbital into spin angular momentum. In a proper choice of pseudogauge, the antisymmetric part of the energy-momentum tensor arises solely from this nonlocal contribution. We show that the collision term vanishes in global equilibrium and that the spin potential is, then, equal to the thermal vorticity. In the nonrelativistic limit, the equations of motion for the energy-momentum and spin tensors reduce to the well-known form for hydrodynamics for micropolar fluids.
During infection the SARS-CoV-2 virus fuses its viral envelope with cellular membranes of its human host. The viral spike (S) protein mediates both the initial contact with the host cell and the subsequent membrane fusion. Proteolytic cleavage of S at the S2′ site exposes its fusion peptide (FP) as the new N-terminus. By binding to the host membrane, the FP anchors the virus to the host cell. The reorganization of S2 between virus and host then pulls the two membranes together. Here we use molecular dynamics (MD) simulations to study the two core functions of the SARS-CoV-2 FP: to attach quickly to cellular membranes and to form an anchor strong enough to withstand the mechanical force during membrane fusion. In eight 10 μs long MD simulations of FP in proximity to endosomal and plasma membranes, we find that FP binds spontaneously to the membranes and that binding proceeds predominantly by insertion of two short amphipathic helices into the membrane interface. Connected via a flexible linker, the two helices can bind the membrane independently, yet binding of one promotes the binding of the other by tethering it close to the target membrane. By simulating mechanical pulling forces acting on the C-terminus of the FP, we then show that the bound FP can bear forces up to 250 pN before detaching from the membrane. This detachment force is more than 10-fold higher than an estimate of the force required to pull host and viral membranes together for fusion. We identify a fully conserved disulfide bridge in the FP as a major factor for the high mechanical stability of the FP membrane anchor. We conclude, first, that the sequential binding of two short amphipathic helices allows the SARS-CoV-2 FP to insert quickly into the target membrane, before the virion is swept away after shedding the S1 domain connecting it to the host cell receptor. Second, we conclude that the double attachment and the conserved disulfide bridge establish the strong anchoring required for subsequent membrane fusion. Multiple distinct membrane-anchoring elements ensure high avidity and high mechanical strength of FP–membrane binding.
Quantum discontinuity fixed point and renormalization group flow of the Sachdev-Ye-Kitaev model
(2021)
We determine the global renormalization group (RG) flow of the Sachdev-Ye-Kitaev (SYK) model. From a controlled truncation of the infinite hierarchy of the exact functional RG flow equations, we identify several fixed points. Apart from a stable fixed point, associated with the celebrated non-Fermi liquid state of the model, we find another stable fixed point related to an integer-valence state. These stable fixed points are separated by a discontinuity fixed point with one relevant direction, describing a quantum first-order transition. Most notably, the fermionic spectrum continues to be quantum critical even at the discontinuity fixed point. This rules out a description of the transition in terms of a local effective Ising variable as is established for classical transitions. We propose an entangled quantum state at phase coexistence as a possible physical origin of this critical behavior.
Famotidine inhibits toll-like receptor 3-mediated inflammatory signaling in SARS-CoV-2 infection
(2021)
Apart from prevention using vaccinations, the management options for COVID-19 remain limited. In retrospective cohort studies, use of famotidine, a specific oral H2 receptor antagonist (antihistamine), has been associated with reduced risk of intubation and death in patients hospitalized with COVID-19. In a case series, nonhospitalized patients with COVID-19 experienced rapid symptom resolution after taking famotidine, but the molecular basis of these observations remains elusive. Here we show using biochemical, cellular, and functional assays that famotidine has no effect on viral replication or viral protease activity. However, famotidine can affect histamine-induced signaling processes in infected Caco2 cells. Specifically, famotidine treatment inhibits histamine-induced expression of Toll-like receptor 3 (TLR3) in SARS-CoV-2 infected cells and can reduce TLR3-dependent signaling processes that culminate in activation of IRF3 and the NF-κB pathway, subsequently controlling antiviral and inflammatory responses. SARS-CoV-2-infected cells treated with famotidine demonstrate reduced expression levels of the inflammatory mediators CCL-2 and IL6, drivers of the cytokine release syndrome that precipitates poor outcome for patients with COVID-19. Given that pharmacokinetic studies indicate that famotidine can reach concentrations in blood that suffice to antagonize histamine H2 receptors expressed in mast cells, neutrophils, and eosinophils, these observations explain how famotidine may contribute to the reduced histamine-induced inflammation and cytokine release, thereby improving the outcome for patients with COVID-19.
HbA1c is the gold standard test for monitoring medium/long term glycemia conditions in diabetes care, which is a critical factor in reducing the risk of chronic diabetes complications. Current technologies for measuring HbA1c concentration are invasive and adequate assays are still limited to laboratory-based methods that are not widely available worldwide. The development of a non-invasive diagnostic tool for HbA1c concentration can lead to the decrease of the rate of undiagnosed cases and facilitate early detection in diabetes care. We present a preliminary validation diagnostic study of W-band spectroscopy for detection and monitoring of sustained hyperglycemia, using the HbA1c concentration as reference. A group of 20 patients with type 1 diabetes mellitus and 10 healthy subjects were non-invasively assessed at three different visits over a period of 7 months by a millimeter-wave spectrometer (transmission mode) operating across the full W-band. The relationship between the W-band spectral profile and the HbA1c concentration is studied using longitudinal and non-longitudinal functional data analysis methods. A potential blind discrimination between patients with or without diabetes is obtained, and more importantly, an excellent relation (R-squared = 0.97) between the non-invasive assessment and the HbA1c measure is achieved. Such results support that W-band spectroscopy has great potential for developing a non-invasive diagnostic tool for in-vivo HbA1c concentration monitoring in humans.
In this letter we report the first multi-differential measurement of correlated pion-proton pairs from 2 billion Au+Au collisions at sNN=2.42 GeV collected with HADES. In this energy regime the population of Δ(1232) resonances plays an important role in the way energy is distributed between intrinsic excitation energy and kinetic energy of the hadrons in the fireball. The triple differential d3N/dMπ±pdpTdy distributions of correlated π±p pairs have been determined by subtracting the πp combinatorial background using an iterative method. The invariant-mass distributions in the Δ(1232) mass region show strong deviations from a Breit-Wigner function with vacuum width and mass. The yield of correlated pion-proton pairs exhibits a complex isospin, rapidity and transverse-momentum dependence. In the invariant mass range 1.1<Minv(GeV/c2)<1.4, the yield is found to be similar for π+p and π−p pairs, and to follow a power law 〈Apart〉α, where 〈Apart〉 is the mean number of participating nucleons. The exponent α depends strongly on the pair transverse momentum (pT) while its pT-integrated and charge-averaged value is α=1.5±0.08st±0.2sy.
For a long time, strong coupling expansions have not been applied systematically in lattice QCD thermodynamics, in view of the success of numerical Monte Carlo studies. The persistent sign problem at finite baryo-chemical potential, however, has motivated investigations using these methods, either by themselves or combined with numerical evaluations, as a route to finite density physics. This article reviews the strategies, by which a number of qualitative insights have been attained, notably the emergence of the hadron resonance gas or the identification of the onset transition to baryon matter in specific regions of the QCD parameter space. For the simpler case of Yang–Mills theory, the deconfinement transition can be determined quantitatively even in the scaling region, showing possible prospects for continuum physics.
We examine the thermodynamic behavior of a static neutral regular (non-singular) black hole enclosed in a finite isothermal cavity. The cavity enclosure helps us investigate black hole systems in a canonical or a grand canonical ensemble. Here we demonstrate the derivation of the reduced action for the general metric of a regular black hole in a cavity by considering a canonical ensemble. The new expression of the action contains quantum corrections at short distances and concludes to the action of a singular black hole in a cavity at large distances. We apply this formalism to the noncommutative Schwarzschild black hole, in order to study the phase structure of the system. We conclude to a possible small/large stable regular black hole transition inside the cavity that exists neither at the system of a classical Schwarzschild black hole in a cavity, nor at the asymptotically flat regular black hole without the cavity. This phase transition seems to be similar with the liquid/gas transition of a Van der Waals gas.
We study the diffusion properties of the strongly interacting quark-gluon plasma (sQGP) and evaluate the diffusion coefficient matrix for the baryon (B), strange (S) and electric (Q) charges—κqq′ (q,q′=B,S,Q) and show their dependence on temperature T and baryon chemical potential μB. The nonperturbative nature of the sQGP is evaluated within the dynamical quasiparticle model (DQPM) which is matched to reproduce the equation of state of the partonic matter above the deconfinement temperature Tc from lattice QCD. The calculation of diffusion coefficients is based on two methods: (i) the Chapman-Enskog method for the linearized Boltzmann equation, which allows to explore nonequilibrium corrections for the phase-space distribution function in leading order of the Knudsen numbers as well as (ii) the relaxation time approximation (RTA). In this work we explore the differences between the two methods. We find a good agreement with the available lattice QCD data in case of the electric charge diffusion coefficient (or electric conductivity) at vanishing baryon chemical potential as well as a qualitative agreement with the recent predictions from the holographic approach for all diagonal components of the diffusion coefficient matrix. The knowledge of the diffusion coefficient matrix is also of special interest for more accurate hydrodynamic simulations.
The present research in high energy physics as well as in the nuclear physics requires the use of more powerful and complex particle accelerators to provide high luminosity, high intensity, and high brightness beams to experiments. With the increased technological complexity of accelerators, meeting the demand of experimenters necessitates a blend of accelerator physics with technology. The problem becomes severe when optimization of beam quality has to be provided in accelerator systems with thousands of free parameters including strengths of quadrupoles, sextupoles, RF voltages, etc. Machine learning methods and concepts of artificial intelligence are considered in various industry and scientific branches, and recently, these methods are used in high energy physics mainly for experiments data analysis.
In Accelerator Physics the machine learning approach has not found a wide application yet, and in general the use of these methods is carried out without a deep understanding on their effectiveness with respect to more traditional schemes or other alternative approaches. The purpose of this PhD research is to investigate the methods of machine learning applied to accelerator optimization, accelerator control and in particular on optics measurements and corrections. Optics correction, maximization of acceptance, and simultaneous control of various accelerator components such as focusing magnets is a typical accelerator scenario. The effectiven- ess of machine learning methods in a complex system such as the Large Hadron Collider, which beam dynamics exhibits nonlinear response to machine settings is the core of the study. This work presents successful application of several machine learning techniques such as clustering, decision trees, linear multivariate models and neural networks to beam optics measurements and corrections at the LHC, providing the guidelines for incorporation of machine learning techniques into accelerator operation and discussing future opportunities and potential work in this field.
The main subject of this thesis is the study of hadron and photon production in relativistic heavy-ion collisions by means of hydrodynamics+transport approaches. Two different kinds of such hybrid approaches are employed in this work, the SMASH-vHLLE-hybrid and a MUSIC+SMASH hybrid. While the former is capable of simulating heavy-ion collisions covering a wide range of collision energies down to √s = 4.3 GeV, reproducing the correct baryon stopping powers, the latter provides a framework to consistently model photon production in the hadronic stage of high-energy heavy-ion collisions.
The SMASH-vHLLE-hybrid is a novel state-of-the-art hybrid approach whose development constitutes a major contribution to this thesis. It couples the hadronic transport SMASH to the 3+1D viscous hydrodynamics approach vHLLE. Therein, SMASH is employed to provide the fluctuating 3D initial conditions and to model the late hadronic rescattering stage, and vHLLE for the fluid dynamical evolution of the hot and dense fireball. The initial conditions are provided on a hypersurface of constant proper time, and the macroscopic evolution of the fireball is carried out down to an energy density of ecrit = 0.5 GeV/fm3, where particlization occurs. Consistency at the interfaces is verified in view of global, on-average quantum number conservation and the SMASH-vHLLE-hybrid is validated by comparison to SMASH+CLVisc as well as UrQMD+vHLLE hybrid approaches. The establishment of the SMASH-vHLLE-hybrid to theoretically describe heavy-ion collisions at intermediate and high collision energies forms a basis for a range of extensions and future research projects. It is further made available to the heavy-ion community by virtue of being published on Github.
The SMASH-vHLLE-hybrid is applied to simulate Au+Au/Pb+Pb collisions between √s = 4.3 GeV and √s = 200.0 GeV. A good agreement with the experimentally measured rapidity and transverse mass spectra is obtained. In particular the baryon stopping dynamics are well reproduced at low, intermediate, and high collision energies. Excitation functions for the mid-rapidity yield and mean transverse momentum of pions, protons and kaons are demonstrated to agree well with their experimentally measured counterpart. These results further validate the approach and provide a solid baseline for potential future studies. The importance of annihilations and regenerations of protons and anti-protons is additionally investigated in Au+Au/Pb+Pb collisions between √s = 17.3 GeV and √s = 5.02 TeV with the SMASH-vHLLE-hybrid. It is found that, regarding the p + p ̄ ↔ 5 π reaction, 20-50% (depending on the rapidity range) of the (anti-)proton yield lost to annihila- tions in the hadronic rescattering stage is restored owing to the back reaction. The back reaction thus constitutes a non-negligible contribution to the final (anti-)proton yield and should not be neglected when modelling the late rescattering stage of heavy-ion collisions.
The MUSIC+SMASH hybrid is a hybrid approach ideally suited to model the production of photons in relativistic heavy-ion collisions. Therein, the macroscopic production of photons in the hadronic stage in MUSIC relies on the identical effective field theories as the photon cross sections implemented in SMASH for the microscopic production. The MUSIC+SMASH hybrid thus provides the first consistent framework to the end of hadronic photon production. It accounts for 2 → 2 scattering processes of the kind π + ρ → π + γ and pion bremsstrahlung processes π + π → π + π + γ. The MUSIC+SMASH hybrid is employed in an ideal 2D setup to systematically assess the importance of non-equliibrium dynamics in the hadronic rescattering stage on mid-rapidity transverse momentum spectra and elliptic flow of photons at RHIC/LHC energies. This is achieved by comparing the outcome of the MUSIC+SMASH hybrid, involving an out-of-equilibrium late rescattering stage, to macroscopically approximating late stage photon production by means of MUSIC, employed down to temperatures well below the switching temperature. It is found that non-equilibrium dynamics have only minor implications for photon transverse momentum spectra, but significantly enhance the photon elliptic flow. At RHIC energies, an enhancement of up to 70%, and at LHC of up to 65% is observed in the non-equilibrium afterburner as compared to its hydrodynamical counterpart. In combination with the large amount of photons produced above the particlization temperature, these differences are modest regarding the transverse momentum spectra, but a significant enhancement of the elliptic flow is observed at low transverse momenta. Below pT ≈ 1.4 GeV, the combined v2 is enhanced by up to 30% at RHIC, and up to 20% at the LHC within the non-equilibrium setup as compared to its approximation via hydrodynamics. Non-equilibrium dynamics in the hadronic rescattering stage are hence important, especially in view of momentum anisotropies at low transverse momenta. These findings thus contribute to the understanding of low-pT photons produced in heavy-ion collisions at RHIC/LHC energies and the MUSIC+SMASH hybrid employed for this study provides a baseline for additional studies regarding photon production in the future.
To summarize, the approaches and frameworks presented in this thesis provide a good baseline for further extensions and studies in order to improve the understanding of hadron and photon production in relativistic heavy-ion collisions across a wide range of collision energies. More broadly, such future studies of hadrons and photons may contribute to enhance the understandig of the properties of the fundamental building blocks of matter, of which everything that surrounds us is made of.
Stationarity of the constituents of the body and of its functionalities is a basic requirement for life, being equivalent to survival in first place. Assuming that the resting state activity of the brain serves essential functionalities, stationarity entails that the dynamics of the brain needs to be regulated on a time-averaged basis. The combination of recurrent and driving external inputs must therefore lead to a non-trivial stationary neural activity, a condition which is fulfiled for afferent signals of varying strengths only close to criticality. In this view, the benefits of working in the vicinity of a second-order phase transition, such as signal enhancements, are not the underlying evolutionary drivers, but side effects of the requirement to keep the brain functional in first place. It is hence more appropriate to use the term 'self-regulated' in this context, instead of 'self-organized'.
Liquid-jet photoelectron spectroscopy was applied to determine the first acid dissociation constant (pKa) of aqueous-phase glucose while simultaneously identifying the spectroscopic signature of the respective deprotonation site. Valence spectra from solutions at pH values below and above the first pKa reveal a change in glucose’s lowest ionization energy upon the deprotonation of neutral glucose and the subsequent emergence of its anionic counterpart. Site-specific insights into the solution-pH-dependent molecular structure changes are also shown to be accessible via C 1s photoelectron spectroscopy. The spectra reveal a considerably lower C 1s binding energy of the carbon site associated with the deprotonated hydroxyl group. The occurrence of photoelectron spectral fingerprints of cyclic and linear glucose prior to and upon deprotonation are also discussed. The experimental data are interpreted with the aid of electronic structure calculations. Our findings highlight the potential of liquid-jet photoelectron spectroscopy to act as a site-selective probe of the molecular structures that underpin the acid–base chemistry of polyprotic systems with relevance to environmental chemistry and biochemistry.
The putative effects of dark matter are most easily explained by a collisionless fluid on cosmological scales and by Modified Newtonian Dynamics (MOND) on galactic scales. Hybrid MOND dark matter models combine the successes of dark matter on cosmological scales and those of MOND on galactic scales. An example of such a model is superfluid dark matter (SFDM) which postulates that this differing behavior with scale is caused by a single underlying substance with two phases. In this thesis, I highlight successful observational tests of SFDM regarding strong lensing and the Milky Way rotation curve. I also discuss three problems due to the double role of the aforementioned single underlying substance and show how these may be avoided. Finally, I introduce a novel Cherenkov radiation constraint for hybrid MOND dark matter models. This constraint is different from standard modified gravity Cherenkov radiation constraints because such hybrid models allow even non-relativistic objects like stars to emit Cherenkov radiation.
Das Feld der Hochenergie-Schwerionenforschung hat sich der Untersuchung des Quark-Gluon-Plasmas (QGP) gewidmet. Ein QGP ist ein sehr heißer und dichter Materiezustand, der kurz nach dem Urknall für einige Mikrosekunden das Universum füllte. Unter diesen extremen Bedingungen sind die fundamentalen Bausteine der Materie, die Quarks und Gluonen, quasi frei, also nicht in Hadronen eingeschlossen, wie es unter normalen Bedingungen der Fall ist. Hadronen sind Teilchen, die aus Quarks und Gluonen bestehen. Die bekanntesten Hadronen sind Protonen und Neutronen, die Bestandteile von Atomkernen, aus denen, zusammen mit Elektronen, die gesamte bekannte Materie aufgebaut ist.
Um ein QGP im Labor zu erzeugen, lässt man ultrarelativistische schwere Ionen, wie zum Beispiel Pb-208-Kerne, aufeinander prallen. Dies geschieht am CERN, dem größten Kernforschungszentrum der Welt. Der Teilchenbeschleuniger, welcher Protonen und Pb-Kerne beschleunigt und zur Kollision bringt, heißt Large Hadron Collider (LHC) und ist mit 27 km Umfang der größte der Welt. Bei einer einzigen Pb-Pb Kollision am LHC werden mehrere Tausend Teilchen und Antiteilchen erzeugt. Das dedizierte Experiment zur Untersuchung von Schwerionenkollisionen am LHC ist ALICE. ALICE ist mit mehreren Teilchendetektoren ausgerüstet, die es ermöglichen, tausende Teilchen gleichzeitig zu messen und zu identifizieren.
Unter den produzierten Teilchen befinden sich auch leichte Atomkerne, wenngleich diese nur sehr selten erzeugt werden. Die Anzahl der produzierten Teilchen pro Teilchensorte hängt nämlich von deren Masse ab. In Pb-Pb Kollisionen am LHC sinkt die Anzahl der produzierten (Anti)kerne exponentiell um einen Faktor 1/330 bei Hinzufügen jedes weiteren Nukleons. Die Menge an produzierten Teilchen pro Spezies stellt Informationen über den Produktionsmechanismus beim Übergang vom QGP zum Hadrongas zur Verfügung. Hierbei sind leichte (Anti)kerne von besonderem Interesse, da sie vergleichsweise groß sind und ihre Bindungsenergie bis zu zwei Größenordnungen kleiner ist als die Temperaturen, die bei der Erzeugung der Hadronen vorherrschen. Es ist bis heute noch nicht verstanden, wie leichte (Anti)kerne bei diesen Bedingungen erzeugt werden und überleben können.
Für diese Arbeit wurden ca. 270 Millionen Pb-Pb Kollisionen bei einer Schwerpunktsenergie von 5,02 TeV, die von ALICE im November 2018 aufgezeichnet wurden, analysiert. Es wurde die Produktion von (Anti)triton und (Anti)alpha untersucht. Wegen ihrer großen Masse werden beide Kerne sehr selten produziert, bei weitem nicht bei jeder Kollision. Antialpha ist der schwerste Antikern, der jemals gemessen wurde. Aufgrund dieser Seltenheit ist die Größe des zur Verfügung stehenden Datensatzes entscheidend. Es war möglich, das erste jemals gemessene Antialpha-Transversalimpulsspektrum zu extrahieren. Auch für (Anti)triton und Alpha wurden Transversalimpulsspektren bestimmt.
Die Ergebnisse wurden mit theoretischen Modellen und anderen ALICE Messungen verglichen.
Am Ende wird in einem Ausblick auf das kürzlich durchgeführte Upgrade der ALICE Spurendriftkammer (TPC) eingegangen. In der nächsten, bald startenden Datennahmeperiode wird der LHC seine Kollisionsrate erheblich erhöhen, was es ermöglichen wird, mehr als 100 mal so viele Daten wie bisher aufzuzeichnen. Hiervon werden die in dieser Arbeit beschriebenen (Anti)triton- und (Anti)alpha-Analysen beachtlich profitieren. Um mit den erheblich höheren Kollisionsraten zurecht zu kommen, mussten einige Detektoren, unter anderem die TPC, maßgeblich erneuert werden. In den ersten beiden Datennahmeperioden wurde die TPC mit Vieldrahtproportionalkammern betrieben. Diese sind allerdings viel zu langsam für die geplanten Kollisionsraten. Deshalb wurden sie im Jahr 2019, während einer langen Betriebspause des LHC, durch Quadrupel-GEM (Gas Electron Multiplier) Folien basierte Auslesekammern ersetzt, welche eine kontinuierliche Auslese der TPC ermöglichen. Da es sich um die erste jemals gebaute GEM TPC im Großformat handelt, war ein umfangreiches Forschungs- und Entwicklungs- (F&E) Programm notwendig, um die GEM Auslesekammern zu charakterisieren und zu testen. Im Rahmen dieses F&E Programms wurden am Anfang dieser Promotion systematische Messungen an einer kleinen Test TPC mit Quadrupel-GEM Auslese, die extra zu diesem Zweck gebaut worden war, durchgeführt. Hierbei wurde der Rückfluss der bei der Gasverstärkung erzeugten Ionen in das Driftvolumen der TPC und die Energieauflösung mit verschiedenen GEM Folien Typen und unterschiedlicher Anordnung gemessen. Das Ziel war, möglichst kleine Ionenrückflüsse bei möglichst guter Energieauflösung zu erreichen. Hierbei musste ein Kompromiss gefunden werden, da die beiden Größen sich gegenläufig verhalten. Es war jedoch möglich, mit mehreren GEM Konfigurationen Spannungseinstellungen zu identifizieren, bei denen beide Größen den gewünschten Anforderungen entsprachen.
The QCD phase-diagram is studied, at finite magnetic field. Our calculations are based on the QCD effective model, the SU(3) Polyakov linear-sigma model (PLSM), in which the chiral symmetry is integrated in the hadron phase and in the parton phase, the up-, down- and strange-quark degrees of freedom are incorporated besides the inclusion of Polyakov loop potentials in the pure gauge limit, which are motivated by various underlying QCD symmetries. The Landau quantization and the magnetic catalysis are implemented. The response of the QCD matter to an external magnetic field such as magnetization, magnetic susceptibility and permeability has been estimated. We conclude that the parton phase has higher values of magnetization, magnetic susceptibility, and permeability relative to the hadron phase. Depending on the contributions to the Landau levels, we conclude that the chiral magnetic field enhances the chiral quark condensates and hence the chiral QCD phase-diagram, i.e. the hadron-parton phase-transition likely takes place, at lower critical temperatures and chemical potentials.
Diese Arbeit beschäftigt sich mit der Wasserkühlung einer normalleitenden CH-Kavität. Insbesondere stellt sich die Frage, ob die im CST Thermal Steady State Solver simulierten Temperaturen mit Messungen während High Power Tests übereinstimmen. Zusätzlich interessiert, inwiefern die Temperatur über die dissipierte Leistung aus dem CST Eigenmode Solver und dem gemessenen Volumenstrom im Kanal abgeschätzt werden kann. In dem Kontext wird auch geklärt, ob die Reihenschaltung der Mantelkanäle den Kühlanforderungen genügt.
Neben Volumenstrom- und Druckmessungen an den in Reihe und parallelgeschalteten Kanälen werden die Leistungs- und Temperaturwerte der Konditionierung in sämtlichen Simulationen aufgegriffen. Indem die Kavität in einzelne Sektionen unterteilt wird und in diesen die dissipierte Leistung mit dem Eigenmode Solver simuliert wird, die ein Kühlkanal abführt, werden die Temperaturerhöhungen direkt berechnet und verglichen.
Zusammengefasst hat sich der Durchfluss in kritischen Bauteilen wie den Stützen durch die Reihenschaltung der Mantelkanäle erhöht und wird damit empfohlen. Es werden die simulierten Temperaturverteilungen gezeigt. Die Näherung über den Eigenmode Solver liefert erneut für die thermisch belasteten Bauteile wie die Stützen präzise Vorhersagen.
Abschließend werden Erfahrungen aus dem Institut in dieser Arbeit zusammengetragen und die Verwendung des Steady State Solver freigegeben.
Topological phases set themselves apart from other phases since they cannot be understood in terms of the usual Landau theory of phase transitions. This fact, which is a consequence of the property that topological phase transitions can occur without breaking symmetries, is reflected in the complicated form of topological order parameters. While the mathematical classification of phases through homotopy theory is known, an intuition for the relation between phase transitions and changes to the physical system is largely inhibited by the general complexity.
In this thesis we aim to get back some of this intuition by studying the properties of the Chern number (a topological order parameter) in two scenarios. First, we investigate the effect of electronic correlations on topological phases in the Green's function formalism. By developing a statistical method that averages over all possible solutions of the manybody problem, we extract general statements about the shape of the phase diagram and investigate the stability of topological phases with respect to interactions. In addition, we find that in many topological models the local approximation, which is part of many standard methods for solving the manybody lattice model, is able to produce qualitatively correct phase transitions at low to intermediate correlations.
We then extend the statistical method to study the effect of the lattice, where we evaluate possible applications of standard machine learning techniques against our information theoretical approach. We define a measure for the information about particular topological phases encoded in individual lattice parameters, which allows us to construct a qualitative phase diagram that gives a more intuitive understanding of the topological phase.
Finally, we discuss possible applications of our method that could facilitate the discovery of new materials with topological properties.
The COLTRIMS Reaction Microscope C-REMI can image the momentum vectors of all emitted charged fragments in an atomic or molecular reactions similar to the bubble chamber in high energy particle physics. C-REMI can detect fragments with “zero” kinetic energy in an ultrahigh vacuum environment by projecting them with weak electromagnetic fields onto position-sensitive detectors. Geometrically a nearly 4π collection solid angle and a nearly 50% efficiency for a fivefold multi-coincidence can be achieved. Measuring time-of-flight and detector position the momenta of the fragments can be measured with excellent resolution (<0.01 a.u.; see A1 in the Appendix). Thus, multivector correlations in momentum space are measured, which provide insight into the entangled dynamics of atomic and molecular quantum systems. From these vector-correlations phases and energies can be deduced which allow for relative time measurements even in the zeptosecond range. C-REMI provides a “spyhole” into the secrets of ultrafast dynamics of atomic and molecular processes. It is applied today around the globe in numerous research projects in physics and chemistry. The purpose for writing this article is to demonstrate the universal application possibilities of C-REMI, and its high multi-coincidence efficiency and high momentum resolution. This paper will not give a review on all milestone experiments performed with C-REMI.
The recent discovery of binary neutron star mergers has opened a new and exciting venue of research into hot and dense strongly interacting matter. For the first time, this elusive state of matter, described by the theory of quantum chromo dynamics, can be studied in two very different environments. On the macroscopic scale, in the collisions of neutron stars; and on the microscopic scale, in collisions of heavy ions at particle collider facilities. We will discuss the conditions that are created in these mergers and the corresponding high energy nuclear collisions. This includes the properties of quantum chromo dynamics matter, that is, the expected equation of state as well as expected chemical and thermodynamic properties of this exotic matter. To explore this matter in the laboratory, a new research prospect is available at the Facility for Antiproton and Ion Research, FAIR. The new facility is being constructed adjacent to the existing accelerator complex of the GSI Helmholtz Centre for Heavy Ion Research at Darmstadt/Germany, expanding the research goals and technical possibilities substantially. The worldwide unique accelerator and experimental facilities of FAIR will open the way for a broad spectrum of unprecedented research supplying a variety of experiments in hadron, nuclear, atomic, and plasma physics as well as biomedical and material science, which will be briefly described.
This work aims at radar sensors in the frequency band from 57 to 64 GHz that can be embedded in wind turbine blades during manufacturing, enabling non-destructive quality inspection directly after production and structural health monitoring (SHM) during the complete service life of the blade. In this paper, we show the fundamental damage detection capability of this sensor technology during fatigue testing of typical rotor blade materials. Therefore, a frequency modulated continuous wave (FMCW) radar sensor is used for damage diagnostics, and the results are validated by simultaneous camera recordings. Here, we focus on the failure modes delamination, fiber waviness (ondulation), and inter-fiber failure. For each failure mode, three samples have been designed and experimentally investigated during fatigue testing. A damage index has been proposed based on residual, that is, differential, signals exploiting measurements from pristine structural conditions. This study shows that the proposed innovative radar approach is able to detect continuous structural degradation for all failure modes by means of gradual signal changes.
This study presents an ultra-wideband, elliptical slot, planar monopole antenna for early breast cancer microwave imaging. The on-body antenna's operation is optimised by direct contact with the patient's skin. With a compact size of 9 × 7 mm, the antenna covers a wide bandwidth from 16 to 24 GHz for reflection coefficients lower than –10 dB. Besides, it also features an electrode for electrical impedance tomography applications. Verification on a volunteer's breast gives an excellent agreement with the simulation for the defined bandwidth. Furthermore, as the first stage of the system's characterisation, pork fat is also used to demonstrate the possibility to enhance the transmission between the antennas within the high loss environment. Those results propose the feasibility of implementing a high-frequency radar system for breast cancer detection.
The cosmological implications of the Covariant Canonical Gauge Theory of Gravity (CCGG) are investigated. CCGG is a Palatini theory derived from first principles using the canonical transformation formalism in the covariant Hamiltonian formulation. The Einstein-Hilbert theory is thereby extended by a quadratic Riemann-Cartan term in the Lagrangian. Moreover, the requirement of covariant conservation of the stress-energy tensor leads to necessary presence of torsion. In the Friedman universe that promotes the cosmological constant to a time-dependent function, and gives rise to a geometrical correction with the EOS of dark radiation. The resulting cosmology, compatible with the ΛCDM parameter set, encompasses bounce and bang scenarios with graceful exits into the late dark energy era. Testing those scenarios against low-z observations shows that CCGG is a viable theory.
Consequences of minimal length discretization on line element, metric tensor, and geodesic equation
(2021)
When minimal length uncertainty emerging from a generalized uncertainty principle (GUP) is thoughtfully implemented, it is of great interest to consider its impacts on gravitational Einstein field equations (gEFEs) and to try to assess consequential modifications in metric manifesting properties of quantum geometry due to quantum gravity. GUP takes into account the gravitational impacts on the noncommutation relations of length (distance) and momentum operators or time and energy operators and so on. On the other hand, gEFE relates classical geometry or general relativity gravity to the energy–momentum tensors, that is, proposing quantum equations of state. Despite the technical difficulties, we intend to insert GUP into the metric tensor so that the line element and the geodesic equation in flat and curved space are accordingly modified. The latter apparently encompasses acceleration, jerk, and snap (jounce) of a particle in the quasi-quantized gravitational field. Finite higher orders of acceleration apparently manifest phenomena such as accelerating expansion and transitions between different radii of curvature and so on.
One of the most challenging problems in solid state systems is the microscopic analysis of electronic correlations. A paramount minimal model that encodes correlation effects is the Hubbard Hamiltonian, which—regardless of its simplicity—is exactly solvable only in a few limiting cases and approximate many-body methods are required for its solution. In this review, an overview on the non-perturbative two-particle self-consistent method (TPSC), which was originally introduced to describe the electronic properties of the single-band Hubbard model, is presented. A detailed derivation of the multi-orbital generalization of TPSC is introduced here and particular features of the method on exemplary interacting models in comparison to dynamical mean-field theory results are discussed.
An investigation of photoelectron angular distributions and circular dichroism of chiral molecules
(2021)
The present work demonstrates the capability of several type of molecular frame photoelectron angular distributions (MFPADs) and their linked chiroptical phenomenon the photoelectron circular dichroism (PECD) to map in great detail the molecular geometry of polyatomic chiral molecules as a function of photoelectron energy. To investigate the influence of the molecular potential on the MFPADs, two chiral molecules were selected, namely 2-(methyl)oxirane (C3H6O, MOx, m = 58,08 uma) and 2-(trifluoromethyl)oxirane (C3H3F3O, TFMOx, m = 112,03 uma). The two molecules differs in one substitutional group and share an oxirane group where the O(1s) electron was directly photoionized with the use of synchrotron radiation in the soft X-ray regime. The direct photoionization of the K-shell electron is well localized in the molecule and it induces the ejection of two or more electrons; the excited system separates into several charged (and eventually neutral) fragments which undergo Coulomb explosion due to their charges. The electrons and the fragments were detected using the COLd Target Recoil Ion Momentum Spectroscopy (COLTRIMS) and the momentum vectors calculated for each fragment belonging from a single ionization. The former method gives the possibility to post-orient molecules in space, giving access to the molecular frame, thus the MFPAD and its related PECD for multiple light propagation direction.
Stereochemistry (from the Greek στερεο- stereo- meaning solid) refers to chemistry in three dimensions. Since most molecules show a three-dimensional structure (3D), stereochemistry pervades all fields of chemistry and biology, and it is an essential point of view for the understanding of chemical structure, molecular dynamics and molecular reactions. The understanding of the chemistry of life is tightly bounded with major discoveries in stereochemistry, which triggered tremendous technical advancements, making it a flourishing field of research since its revolutionary introduction in late 18th century. In chemistry, chirality is a brunch of stereochemistry which focuses on objects with the peculiar geometrical property of not being superimposable to their mirror-images. The word chirality is derived from the Greek χειρ for “hand”, and the first use of this term in chemistry is usually attributed to Lord Kelvin who called during a lecture at the Oxford University Junior Scientific Club in 1893 “any geometrical figure, or group of points, “chiral”, and say that it has chirality if its image in a plane mirror, ideally realized, cannot be brought to coincide with itself.”. Although the latter is usually considered as the birth of the word chirality, the concept underlying it was already present in several fields of science (above all mathematics), already proving the already multidisciplinary relevance of chirality across many field of science and beyond. Nature shows great examples of chiral symmetry on all scales. Empirically, it is possible to observe it at macroscopic scale (e.g. distribution of rotations of galaxies), down to the microscopic scale (e.g. structure of some plankton species), but it is at the molecular level where the number gets remarkable: most of the pharmaceutical drugs, food fragrances, pheromones, enzymes, amino acids and DNA molecules, in fact, are chiral. Moreover, the concept of chirality goes far beyond the mere spatial symmetry of objects being crucially entangled with the fundamental properties of physical forces in nature. The symmetry breaking, namely the different physical behaviour of a two chiral systems upon the same stimuli, is considered to be one of the best explanation for the long standing questions of homochirality in biological life, and ultimately to the chemical origin of life on Earth as we know it. Our organism shows high enantio-selectivity towards specific compounds ranging from drugs, to fragrances. Over 800 odour molecules commonly used in food and fragrance industries have been identified as chiral and their enantiomeric forms are perceived to have very different smells, as the well-know example of D- and L- limonene. Similarly, responses to pharmaceuticals drugs can be enantiomer specific, and in fact about 60 % the drugs currently on the market are chiral compounds, and nearly 90 % of them are sold as racemates. The same degree of enantio-selectivity is observed in the communications systems of plants and insects. Plants produce lipophilic liquids with high vapour pressure called plant volatiles (PVs) which are synthesized via different enzymes called tarpene synthases that are usually chiral. Chiral molecules and chiral effects have a strong impact on all the fields of science with exciting developments ranging from stereo-selective synthesis based on heterogeneous enantioselective catalysis, to optoelctronics, to photochemical asymmetric synthesis, and chiral surface science, just to cite a few.
Chiral molecules come in two forms called enantiomers. Their almost identical chemical and physical properties continue to pose technical challenges concerning the resolution of racemic mixtures, the determination of the enantiomeric excess, and the direct determination of the absolute configuration of an enantiomer. ...
Nano-granular metals are materials that fall into the general class of granular electronic systems in which the interplay of electronic correlations, disorder and finite size effects can be studied. The charge transport in nano-granular metals is dominated by thermally-assisted, sequential and correlated tunneling over a temperature-dependent number of metallic grains. Here we study the frequency-dependent conductivity (AC conductivity) of nano-granular Platinum with Pt nano-grains embedded into amorphous carbon (C). We focus on the transport regime on the insulating side of the insulator metal transition reflected by a set of samples covering a range of tunnel-coupling strengths. In this transport regime polarization contributions to the AC conductivity are small and correlation effects in the transport of free charges are expected to be particularly pronounced. We find a universal behavior in the frequency dependence that can be traced back to the temperature-dependent zero-frequency conductivity (DC conductivity) of Pt/C within a simple lumped-circuit analysis. Our results are in contradistinction to previous work on nano-granular Pd/ZrO2ZrO2 in the very weak coupling regime where polarization contributions to the AC conductivity dominated. We describe possible future applications of nano-granular metals in proximity impedance spectroscopy of dielectric materials.
In this thesis we investigate the thermodynamic and dynamic properties of the D-dimensional quantum Heisenberg ferromagnet within the spin functional renormalization group (FRG); a
formalism describing the evolution of the system’s observables as the magnetic exchange inter-action is artificially deformed. Following an introduction providing a self contained summary of the conceptual and mathematical background, we present the spin FRG as developed by Krieg and Kopietz in references [1] and [2] in chapter two. Thereto, the generating functional of the imaginary time-spin correlation functions and its exact flow equation describing the deformation process of the exchange interaction are introduced. In addition, it is highlighted that - in contrast to conventional field-theoretic FRG approaches - the related Legendre trans-formed functional cannot be defined if the exchange interaction is initially switched off. Next, we show that this limitation can be circumvented within an alternativ hybrid approach, which treats transverse and longitudinal spin fluctuations differently. The relevant functionals are introduced and the relations of the corresponding functional Taylor coefficients with the spin correlation functions are discussed. Lastly, the associated flow equations are derived and the possibility of explicit or spontaneous symmetry breaking is taken into account.
In chapter three, we benchmark the hybrid formalism against a calculation of the thermo-dynamic properties of the one and two-dimensional Heisenberg model at low temperatures T and finite magnetic field H. For this purpose, we devise an anisotropic deformation scheme of the exchange interaction which allows for a controlled truncation of the infinite hierarchy of FRG flow equations. Thereby, contact with mean-field and spin-wave theory is made and the violation of the Mermin-Wagner theorem is discussed. To fulfill the latter, the truncation scheme is then complemented by a Ward identity relating the transverse self-energy and the magnetization. The resulting magnetization M (H, T ) and isothermal susceptibility χ(H, T ) are in quantitative agreement with the literature and the established behavior of the transverse correlation length and the zero-field susceptibility close to the critical point is qualitatively reproduced in the limit H → 0.
Finally, we investigate the longitudinal dynamics at low temperatures. To this end, the hierarchy of flow equations is solved within the same anisotropic deformation scheme complemented by an expansion in the inverse interaction range, and the resulting longitudinal dynamic structure factor is calculated within a low-momentum expansion. In D = 3, the large phase space accessible for the decay into transverse magnons yields only a broad hump centered at zero frequency whose width scales linearly in momentum. In contrast, at low temperatures and in a certain range of magnetic fields, a well-defined quasiparticle peak with linear dispersion emerges in D ≤ 2, which we identify as zero-magnon sound. Sound velocity and damping are discussed as a function of temperature and magnetic field, and the relevant momentum-frequency window is estimated and compared to the hydrodynamic
second-magnon regime.
When a nanoparticle is irradiated by an intense laser pulse, it turns into a nanoplasma, a transition that is accompanied by many interesting nonequilibrium dynamics. So far, most experiments on nanoplasmas use ion measurements, reflecting the outside dynamics in the nanoparticle. Recently, the direct observation of the ultrafast structural dynamics on the inside of the nanoparticle also became possible with the advent of x-ray free electron lasers (XFELs). Here, we report on combined measurements of structural dynamics and speeds of ions ejected from nanoplasmas produced by intense near-infrared laser irradiations, with the control of the initial plasma conditions accomplished by widely varying the laser intensity (9×1014 W/cm2 to 3×1016 W/cm2). The structural change of nanoplasmas is examined by time-resolved x-ray diffraction using an XFEL, while the kinetic energies of ejected ions are measured by an ion time-of-fight method under the same experimental conditions. We find that the timescale of crystalline disordering in nanoplasmas strongly depends on the laser intensity and scales with the inverse of the average speed of ions ejected from the nanoplasma. The observations support a recently suggested scenario for nanoplasma dynamics in the wide intensity range, in which crystalline disorder in nanoplasmas is caused by a rarefaction wave propagating at a speed comparable with the average ion speed from the surface toward the inner crystalline core. We demonstrate that the scenario is also applicable to nanoplasma dynamics in the hard x-ray regime. Our results connect the outside nanoplasma dynamics to the loss of structure inside the sample on the femtosecond timescale.
Destruction of the cosmic γ-ray emitter 26Al in massive stars: study of the key 26Al(n,p) reaction
(2021)
The 26Al(n,p)26Mg reaction is the key reaction impacting on the abundances of the cosmic γ-ray emitter 26Al produced in massive stars and impacts on the potential pollution of the early solar system with 26Al by asymptotic giant branch stars. We performed a measurement of the 26Al(n,p)26Mg cross section at the high-flux beam line EAR-2 at the n_TOF facility (CERN). We report resonance strengths for eleven resonances, nine being measured for the first time, while there is only one previous measurement for the other two. Our resonance strengths are significantly lower than the only previous values available. Our cross-section data range to 150 keV neutron energy, which is sufficient for a reliable determination of astrophysical reactivities up to 0.5 GK stellar temperature.
We present the first holographic simulations of non-equilibrium steady state formation in strongly coupled N=4 SYM theory in 3+1 dimensions. We initially join together two thermal baths at different temperatures and chemical potentials and compare the subsequent evolution of the combined system to analytic solutions of the corresponding Riemann problem and to numeric solutions of ideal and viscous hydrodynamics. The time evolution of the energy density that we obtain holographically is consistent with the combination of a shock and a rarefaction wave: A shock wave moves towards the cold bath, and a smooth broadening wave towards the hot bath. Between the two waves emerges a steady state with constant temperature and flow velocity, both of which are accurately described by a shock+rarefaction wave solution of the Riemann problem. In the steady state region, a smooth crossover develops between two regions of different charge density. This is reminiscent of a contact discontinuity in the Riemann problem. We also obtain results for the entanglement entropy of regions crossed by shock and rarefaction waves and find both of them to closely follow the evolution of the energy density.
New drugs are urgently needed to combat the global TB epidemic. Targeting simultaneously multiple respiratory enzyme complexes of Mycobacterium tuberculosis is regarded as one of the most effective treatment options to shorten drug administration regimes, and reduce the opportunity for the emergence of drug resistance. During infection and proliferation, the cytochrome bd oxidase plays a crucial role for mycobacterial pathophysiology by maintaining aerobic respiration at limited oxygen concentrations. Here, we present the cryo-EM structure of the cytochrome bd oxidase from M. tuberculosis at 2.5 Å. In conjunction with atomistic molecular dynamics (MD) simulation studies we discovered a previously unknown MK-9-binding site, as well as a unique disulfide bond within the Q-loop domain that defines an inactive conformation of the canonical quinol oxidation site in Actinobacteria. Our detailed insights into the long-sought atomic framework of the cytochrome bd oxidase from M. tuberculosis will form the basis for the design of highly specific drugs to act on this enzyme.
As a first step towards a realistic phenomenological description of vector and axial-vector mesons in nuclear matter, we calculate the spectral functions of the ρ and the a1 meson in a chiral baryon-meson model as a low-energy effective realization of QCD, taking into account the effects of fluctuations from scalar mesons, nucleons, and vector mesons within the functional renormalization group (FRG) approach. The phase diagram of the effective hadronic theory exhibits a nuclear liquid-gas phase transition as well as a chiral phase transition at a higher baryon-chemical potential. The in-medium ρ and a1 spectral functions are calculated by using the previously introduced analytically-continued FRG (aFRG) method. Our results show strong modifications of the spectral functions—in particular near the critical endpoints of both phase transitions—which may well be of relevance for electromagnetic rates in heavy-ion collisions or neutrino emissivities in neutron-star merger events.
In two-dimensional (2D) NbSe2 crystal, which lacks inversion symmetry, strong spin-orbit coupling aligns the spins of Cooper pairs to the orbital valleys, forming Ising Cooper pairs (ICPs). The unusual spin texture of ICPs can be further modulated by introducing magnetic exchange. Here, we report unconventional supercurrent phase in van der Waals heterostructure Josephson junctions (JJs) that couples NbSe2 ICPs across an atomically thin magnetic insulator (MI) Cr2Ge2Te6. By constructing a superconducting quantum interference device (SQUID), we measure the phase of the transferred Cooper pairs in the MI JJ. We demonstrate a doubly degenerate nontrivial JJ phase (ϕ), formed by momentum-conserving tunneling of ICPs across magnetic domains in the barrier. The doubly degenerate ground states in MI JJs provide a two-level quantum system that can be utilized as a new dissipationless component for superconducting quantum devices. Our work boosts the study of various superconducting states with spin-orbit coupling, opening up an avenue to designing new superconducting phase-controlled quantum electronic devices.
In local scalar quantum field theories at finite temperature correlation functions are known to satisfy certain nonperturbative constraints, which for two-point functions in particular implies the existence of a generalization of the standard Källén-Lehmann representation. In this work, we use these constraints in order to derive a spectral representation for the shear viscosity arising from the thermal asymptotic states, η0. As an example, we calculate η0 in ϕ4 theory, establishing its leading behavior in the small and large coupling regimes.
The first part of this work addresses the automatic online tuning of transfer lines in particle accelerator facilities. In the second part the focus lies on the automatic construction and optimisation of such transport lines. It can be shown that genetic algorithms can be used very well for optimisation in both cases. Automatic online tuning can be performed very efficiently at accelerators under certain boundary conditions and is particularly well suited for initial beam commissioning with low intensity pilot beams. The construction of transfer lines can also be formulated and solved as an minimisation problem with an adopted parameterisation. Thereby, both the imaging properties of the beam transport and the robustness against error studies can be optimised at the same time.
Ziel dieser Dissertation ist es, die Gleichgewichts- und Nichtgleichgewichts-Eigenschaften des stark wechselwirkenden QGP-Mediums nahe dem Phasenübergang unter extremen Bedingungen von hohen T und hohen Baryonendichten mit Hilfe der kinetischen Theorie im Rahmen von effektiven Modellen zu untersuchen. Wir werden zunächst die thermodynamischen und Transporteigenschaften des QGPs in der Nähe des Gleichgewichts auf der Basis des DQPM im Bereich moderater chemischer Baryonenpotentiale μB ≥ 0.5 GeV untersuchen. Insbesondere werden die EoS und die Schallgeschwindigkeit sowie die Transportkoeffizienten des QGP auf der Grundlage des DQPM bei endlichen T und μB berechnet. Transportkoeffizienten sind besonders interessant, da sie Informationen über die Wechselwirkungen im Medium erlauben, das im Gleichgewicht durch eine Temperatur T und ein chemisches Potential μB charakterisiert werden kann. Unter Berücksichtigung der Transportkoeffizienten und der EoS der QGP-Phase vergleichen wir unsere Ergebnisse mit verschiedenen Resultaten aus der Literatur, in denen Transportkoeffizienten des QGPs auf Basis von effektiven Modellen vorwiegend bei Null oder kleinem chemischen Potentialen untersucht wurden.
Darüber hinaus werden in Kapitel 3 die Gleichgewichtseigenschaften des QGPs und insbesondere die Auswirkungen der μB-Abhängigkeit der thermodynamischen und Transporteigenschaften des QGPs im Rahmen des erweiterten PHSD-Transportansatzes untersucht, der die vollständige Entwicklung des Systems einschließlich der partonischen Phase umfasst. Die Entwicklung des PHSD-Transportansatzes wird in der partonischen Phase erweitert, indem explizit die gesamt- und differentiellen partonischen Streuquerschnitte auf der Grundlage des DQPM berechnet und bei der tatsächlichen Temperatur T und dem baryonischen chemischen Potential μB in jeder einzelnen Raum-Zeit-Zelle, in der die partonische Streuung stattfindet, ausgewertet werden.
Um die Spuren der μB-Abhängigkeit des QGPs in den Observablen zu untersuchen, werden die Ergebnisse von PHSD5.0 (mit μB-Abhängigkeiten) mit den Ergebnissen von PHSD5.0 für μB = 0 sowie mit PHSD4.0, in dem die Massen/Breiten der Quarks und Gluonen sowie deren Wechselwirkungsquerschnitte nur von T abhängen, verglichen. Wir diskutieren die PHSD-Ergebnisse für verschiedene Observablen: (i) Rapiditäts- und pT -Verteilungen von identifizierten Hadronen für symmetrische Au+Au- und Pb+Pb- Kollisionen bei Energien von 30 AGeV (zukünftige NICA-Energie) sowie für die RHIC-Spitzenenergie von √sNN = 200 GeV; (ii) gerichteter Fluss v1 von identifizierten Hadronen für Au + Au bei invarianter Energie √sNN = 27 GeV und 200 GeV; (iii) elliptischer Fluss v2 der identifizierten Hadronen für Au+Au bei invarianten Energien √sNN = 27 und 200 GeV. Der Vergleich der "Bulk"-Observablen für Au+Au-Kollisionen innerhalb der drei PHSD-Einstellungen hat gezeigt, dass sie eine recht geringe Empfindlichkeit gegenüber den μB -Abhängigkeiten der Partoneigenschaften (Massen und Breiten) und ihrer Wechselwirkungsquerschnitte aufweisen, sodass die Ergebnisse von PHSD5.0 mit und ohne μB sehr nahe beieinander liegen. Nur im Fall von Kaonen, Antiprotonen ̄p und Antihyperonen ̄Λ + ̄Σ0 konnte ein kleiner Unterschied zwischen PHSD4.0 und PHSD5.0 bei den höchsten SPS- und RHIC-Energien festgestellt werden.
Wir finden nur geringe Unterschiede zwischen den Ergebnissen von PHSD4.0 und PHSD5.0 für die hier betrachteten hadronischen Observablen sowohl bei hohen als auch bei mittleren Energien. Dies hängt damit zusammen, dass bei hohen Energien, wo die Materie vom QGP dominiert wird, ein sehr kleines chemisches Baryonenpotential μB in zentralen Kollisionen bei mittlerer Rapidität gemessen wird, während mit abnehmender Energie und größerem μB der Anteil des QGPs rapide abnimmt, sodass die endgültigen Beobachtungswerte insgesamt von den Hadronen dominiert werden, die an der hadronischen Rückstreuung teilgenommen haben, und somit die Information über ihren QGP-Ursprung verwaschen oder verloren geht.
In Kapitel 4 betrachten wir die Transportkoeffizienten von QGP-Materie im erweiterten Polyakov-NJL-Modell entlang der Übergangslinie für moderate Werte des chemischen Baryonenpotenzials 0 ≤ μB ≤ 0.9 GeV sowie in der Nähe des kritischen Endpunkts(CEP) und bei großem chemischen Baryonenpotenzial μB = 1.2 GeV, wo ein Phasenübergang erster Ordnung stattfindet. Wir untersuchen, wie die Natur der Freiheitsgrade die Transporteigenschaften des QGPs beeinflusst. Darüber hinaus demonstrieren wir die Auswirkungen des Phasenübergangs erster Ordnung und des CEP auf die Transportkoeffizienten im dekonfinierten QCD-Medium.
Darüber hinaus wird in Kapitel 5 eine phänomenologische Erweiterung des DQPM auf große baryonchemische Potentiale μB einschließlich der Region mit einem möglichen CEP und späterem Phasenübergang erster Ordnung betrachtet. Eines der wichtigsten Merkmale des Modells ist das Auftreten einer ’kritischen‘ Skalierung in der Nähe des CEP. Das Hauptziel des vorgestellten Modells besteht darin, die mikroskopischen und makroskopischen Eigenschaften der partonischen Freiheitsgrade für den Bereich des Phasendiagramms bereitzustellen, der durch moderates T und moderates oder hohes μB gekennzeichnet ist.
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The main focus of research in the field of high-energy heavy-ion physics is the study of the quark-gluon plasma (QGP). Topic of the present work is the measurement of electron-positron pairs (dielectrons), which grant direct access to some of the key properties of this state of matter, since after their formation they leave the hot and dense medium without significant interaction. In particular, the measurement of the initial QGP temperature is considered a "holy grail" of heavy-ion physics. Therefore, in addition to the analysis of existing data, a feasibility study has been conducted to determine to which extent this goal would be achievable by upgrading the ALICE experiment at CERN.
Dielectrons are produced during all stages of a heavy-ion collision, with their invariant mass reflecting the amount of energy available at the time of their formation. Dielectrons of highest mass are thus produced in the initial scatterings of the colliding nuclei by quark-antiquark annihilation. Correlated electron-positron pairs can also emerge from the decay chains of early-produced pairs of heavy-flavour (HF) particles. During the QGP stage and at the beginning of the hadronic phase, the system emits thermal radiation in the form of photons and dielectrons, which carry information about the medium temperature to the observer. In the final stage of the collision, decays of light-flavour (LF) hadrons produce additional contributions to the dielectron spectrum.
The present work is based on early data from the ALICE experiment recorded from lead-lead collisions at a center-of-mass energy of 2.76 TeV. Due to the limited amount of data, a focus is placed on achieving high efficiencies throughout the analysis. To this end, a special electron identification strategy is developed and a custom track selection applied, together resulting in a tenfold increase in pair efficiency. The dielectron spectrum is evaluated on a statistical basis, using a pair prefilter, which is optimized based on two signal quality criteria, to reduce the fraction of electrons and positrons from unwanted sources at minimum signal loss. In addition, an artifact of the track reconstruction is exploited to suppress pairs from photon conversions and to correct the dielectron yield for a contribution from different-conversion pairs. The main signal uncertainty is extracted from the deviation between results of 20 analysis settings and amounts to 20% in most of the studied kinematic range.
For comparison with the analysis results, a hadronic cocktail consisting of the LF and HF contributions is simulated, which can reasonably well describe the measured dielectron production, with a hint of an enhancement at low invariant mass. Two approaches to model the in-medium modification of the heavy-flavour are followed, resulting in up to 50% suppression, which creates some additional space for a thermal contribution at intermediate mass.
For a complete comparison between experimental data and theoretical expectation, two model calculations are consulted. The Thermal Fireball Model provides predictions for thermal dielectron radiation from the QGP and hadron gas. The data tends to be better described with these additional thermal contributions. For a comparison with a prediction by the UrQMD model, the HF component of the cocktail is subtracted from the data. This results in better agreement if the HF suppression by in-medium effects is taken into account.
The feasibility study in this work has served as a physical motivation for the ALICE upgrade for LHC Run 3. The precision with which the early temperature of the QGP can be determined via dielectrons is chosen as key observable. A multitude of individual contributions are merged into a fully modeled dielectron analysis. The resulting signal-to-background ratio represents some of the expected systematic uncertainties, while from the significance combined with the planned number of lead-lead collisions a realistic "measurement" with statistical fluctuations around the expected dielectron signal is generated using a Poisson sampling technique. Since the HF yield exceeds the QGP thermal radiation by about an order of magnitude, an additional analysis step exploiting the enhanced track reconstruction is introduced to reduce its contribution by up to a factor of five. The resulting reduction in pair efficiency is overcompensated by an up to hundred times higher collision rate. The entire cocktail is then subtracted from the sampled data to isolate the thermal excess yield. The final analysis of this spectrum shows that the inverse slope of the model prediction, which depends directly on the QGP temperature, can be reproduced within statistical and systematic uncertainties of about 10%.
The promising results of this study have contributed on the one hand to the realization of the ALICE upgrade and to a design decision for the new Inner Tracking System, and at the same time represent exciting predictions for upcoming measurements.
Die vorliegende Dissertation stellt die Strahldynamikdesigns zweier Hochfrequenzquadrupol-Linearbeschleuniger bzw. Radio Frequency Quadrupoles (RFQs) vor: das fur den RFQ des Protonen-Linearbeschleunigers (p-Linac) des FAIR2-Projekts an der GSI3 Darmstadt sowie einen ersten Designentwurf für einen kompakten RFQ, der u.a. zur Erzeugung von Radioisotopen für medizinische Zwecke genutzt werden könnte. Der Schwerpunkt liegt auf dem ersten Design.
Model frameworks, based on Floquet theory, have been shown to produce effective tools for accurately predicting phase-noise response of single (free-running) oscillator systems. This method of approach, referred to herein as macro-modeling, has been discussed in several highly influential papers and now constitutes an established branch of modern circuit theory. The increased application of, for example, injection-locked oscillators and oscillator arrays in modern communication systems has subsequently exposed the demand for similar rigorous analysis tools aimed at coupled oscillating systems. This paper presents a novel solution in terms of a macro-model characterizing the phase-response of synchronized coupled oscillator circuits and systems perturbed by weak noise sources. The framework is generalized and hence applicable to all circuit configurations and coupling topologies generating a synchronized steady-state. It advances and replaces the phenomenological descriptions currently found in the published literature pertaining to this topic and, as such, represents a significant breakthrough w.r.t. coupled oscillator noise modeling. The proposed model is readily implemented numerically using standard routines.
For finite baryon chemical potential, conventional lattice descriptions of quantum chromodynamics (QCD) have a sign problem which prevents straightforward simulations based on importance sampling.
In this thesis we investigate heavy dense QCD by representing lattice QCD with Wilson fermions at finite temperature and density in terms of Polyakov loops.
We discuss the derivation of $3$-dimensional effective Polyakov loop theories from lattice QCD based on a combined strong coupling and hopping parameter expansion, which is valid for heavy quarks.
The finite density sign problem is milder in these theories and they are also amenable to analytic evaluations.
The analytic evaluation of Polyakov loop theories via series expansion techniques is illustrated by using them to evaluate the $\SU{3}$ spin model.
We compute the free energy density to $14$th order in the nearest neighbor coupling and find that predictions for the equation of state agree with simulations to $\mathcal{O}(1\%)$ in the phase were the (approximate) $Z(3)$ center symmetry is intact.
The critical end point is also determined but with less accuracy and our results agree with numerical results to $\mathcal{O}(10\%)$.
While the accuracy for the endpoint is limited for the current length of the series, analytic tools provide valuable insight and are more flexible.
Furthermore they can be generalized to Polyakov-loop-theories with $n$-point interactions.
We also take a detailed look at the hopping expansion for the derivation of the effective theory.
The exponentiation of the action is discussed by using a polymer expansion and we also explain how to obtain logarithmic resummations for all contributions, which will be achieved by employing the finite cluster method know from condensed matter physics.
The finite cluster method can also be used to evaluate the effective theory and comparisons of the evaluation of the effective action and a direction evaluation of the partition function are made.
We observe that terms in the evaluation of the effective theory correspond to partial contractions in the application of Wick's theorem for the evaluation of Grassmann-valued integrals.
Potential problems arising from this fact are explored.
Next to next to leading order results from the hopping expansion are used to analyze and compare the onset transition both for baryon and isospin chemical potential.
Lattice QCD with an isospin chemical potential does not have a sign problem and can serve as a valuable cross-check.
Since we are restricted by the relatively short length of our series, we content ourselves with observing some qualitative phenomenological properties arising in the effective theory which are relevant for the onset transition.
Finally, we generalize our results to arbitrary number of colors $N_c$.
We investigate the transition from a hadron gas to baryon condensation and find that for any finite lattice spacing the transition becomes stronger when $N_c$ is increased and to be first order in the limit of infinite $N_c$.
Beyond the onset, the pressure is shown to scale as $p \sim N_c$ through all available orders in the hopping expansion, which is characteristic for a phase termed quarkyonic matter in the literature.
Some care has to be taken when approaching the continuum, as we find that the continuum limit has to be taken before the large $N_c$ limit.
Although we currently are unable to take the limits in this order, our results are stable in the controlled range of lattice spacings when the limits are approached in this order.
Computational workflow optimization for magnetic fluctuation measurements of 3D nano-tetrapods
(2021)
The detailed understanding of micro–and nanoscale structures, in particular their magnetization dynamics, dominates contemporary solid–state physics studies. Most investigations already identified an abundance of phenomena in one–and two–dimensional nanostructures. The following thesis focuses on the magnetic fingerprint of three–dimensional CoFe nano–magnets, specifically the temporal development of their hysteresis loop. These nano–magnets were grown in a tetrahedral pattern on top of a highly susceptible home–build GaAs/AlGaAs micro–Hall sensor using focused electron beam induced deposition (FEBID).
During the measurements, utmost efforts were employed to exemplify current best research practices. The data life cycle of the present thesis is based upon open–source data science tools and packages. Data acquisition and analysis required self–written automated algorithms to handle the extensive quantity of data. Existing instrumental-controlling software was improved, and new Python packages were devised to analyze and visualize the gathered data. The open–source Python data analysis framework (ana) was developed to facilitate computational reproducibility. This framework transparently analyses and visualizes the gathered data automatically using Continuous Analysis tools based on GitLab and Continuous Integration. This automatization uses bespoke scripts combined with virtualization tools like Docker to facilitate reproducible and device–independent results.
The hysteresis loops reveal distinct differences in subsequently measured loops with identical initial experimental parameters, originating from the nano–magnet’s magnetic noise. This noise amplifies in regions where switching processes occur. In such noise–prone regions, the time–dependent scrutinization reveals presumably thermally induced metastable magnetization states. The frequency–dependent power spectral density uncovers a characteristic 1/f² behavior at noise–prone regions with metastable magnetization states.
In this roadmap article, we have focused on the most recent advances in terahertz (THz) imaging with particular attention paid to the optimization and miniaturization of the THz imaging systems. Such systems entail enhanced functionality, reduced power consumption, and increased convenience, thus being geared toward the implementation of THz imaging systems in real operational conditions. The article will touch upon the advanced solid-state-based THz imaging systems, including room temperature THz sensors and arrays, as well as their on-chip integration with diffractive THz optical components. We will cover the current-state of compact room temperature THz emission sources, both optolectronic and electrically driven; particular emphasis is attributed to the beam-forming role in THz imaging, THz holography and spatial filtering, THz nano-imaging, and computational imaging. A number of advanced THz techniques, such as light-field THz imaging, homodyne spectroscopy, and phase sensitive spectrometry, THz modulated continuous wave imaging, room temperature THz frequency combs, and passive THz imaging, as well as the use of artificial intelligence in THz data processing and optics development, will be reviewed. This roadmap presents a structured snapshot of current advances in THz imaging as of 2021 and provides an opinion on contemporary scientific and technological challenges in this field, as well as extrapolations of possible further evolution in THz imaging.
Presolar grains and their isotopic compositions provide valuable constraints to AGB star nucleosynthesis. However, there is a sample of O- and Al-rich dust, known as group 2 oxide grains, whose origin is difficult to address. On the one hand, the 17O/16O isotopic ratios shown by those grains are similar to the ones observed in low-mass red giant stars. On the other hand, their large 18O depletion and 26Al enrichment are challenging to account for. Two different classes of AGB stars have been proposed as progenitors of this kind of stellar dust: intermediate mass AGBs with hot bottom burning, or low mass AGBs where deep mixing is at play. Our models of low-mass AGB stars with a bottom-up deep mixing are shown to be likely progenitors of group 2 grains, reproducing together the 17O/16O, 18O/16O and 26Al/27Al values found in those grains and being less sensitive to nuclear physics inputs than our intermediate-mass models with hot bottom burning.
Neurons are cells with a highly complex morphology; their dendritic arbor spans up to thousands of micrometers. This extended arbor poses a challenge for the logistics of neuronal processes: mRNA, proteins, and organelles have to be transported to dendrites, hundreds of micrometers away from the soma. This thesis aims to calculate the minimum number of proteins needed to populate the dendritic trees for different scenarios.
In chapter 2, I analyzed the ability of different mechanisms to populate the dendritic arbor. I started from the solution of the diffusion equation in Sec. 2.1, then I included the contribution of active transport in Sec. 2.2 and showed how it could have either the effect of increasing the effective diffusion coefficient or of introducing a bias in the diffusion process. In Sec. 2.3 I studied the spatial distribution of locally synthesized protein, accordingly with actively and passively transported mRNA. In Sec. 2.5, I derived the boundary condition for branches showing a qualitatively different behavior of surface and cytoplasmic proteins induced by the medium’s dimensionality in which they diffuse.
In chapter 3, I introduced the concept of protein requirement, defined as the minimum number of proteins that the neuron needs to produce to provide at least one protein to each micrometer of the dendritic arbor. In Sec. 3.1, I derived the protein requirement for diffusive proteins for somatic translation and constant translation in the dendritic arbor. In Sec. 3.2, I analyzed numerically the protein requirement in the case of actively transported protein synthesized in the soma, and, in Sec. 3.3, in the case of actively transported proteins synthesized in the dendritic arbor. In Sec. 3.4, I analyzed the protein requirement of protein synthesized in the dendrite accordingly with the distribution of mRNA described in Sec. 3.3 and 3.2. In Sec. 3.5, I derived the protein requirement for a single branch and purely diffusive proteins.
In chapter 4, I analyzed the relation between the radii of the three afferent dendrites in a branch, their length, and the diffusion length of a protein. In Sec. 4.1 I derived the optimal ratio between the radii of the daughter dendrites that minimizes the protein requirement. In Sec. 4.3 I introduced the 3/2− Rall Rule and in Sec. 4.5 its generalization. Finally, I used those rules to estimate the fraction of proteins diffusing away from and toward the soma.
In chapter 5, I analyzed the radii distribution for three categories of neurons: cultured hippocampal neurons in Sec. 5.1, stomatogastric ganglia neuron in Sec. 5.2, and 3DEM reconstructed prefrontal pyramidal neurons in Sec. 5.3. For each of these three classes, I analyzed the distribution of radii, Rall exponents, and the probability ratio. For most of them, I found that the probability of a protein diffusing away from the soma is higher for surface proteins than for cytoplasmic ones. I quantified this with a parameter called surface bias.
In Chapter 6, I analyzed the fluorescent ratio imaged by our collaborators Anne-Sophie Hafner, for a surface protein, GFP::Nlg, and a soluble one, GFP, in cultured hippocampal neurons, and I compared the fluorescent ratio with the probability ratio obtained in 5.1, finding that they are in good agreement.
In chapter 7, I compared the real dendritic morphologies imaged by one of our collaborators Ali Karimi with the optimal branching rule obtained in Sec. 4.1 and I calculated the cost for not having optimal branching radii.
Finally, in Chapter 8, I used the knowledge of the branching statistics gathered in 5.3 to simulate the protein profile on three different classes of neurons: pyramidal neurons, granule neuron, and Purkinje neurons. I compared the protein profile for surface and cytoplasmic neurons for each morphology for two different values of the diffusion length: λ = 109µm and λ = 473µm, both for optimized radii and symmetrical radii. I showed how the radii optimization reduces the protein requirement of a factor 10 4 for pyramidal neurons.
Prof. (em.) Dr. Bruno Lüthi
(2021)
Particle collisions provide insight into the structure of matter and the interaction of its constituents. Furthermore, they also allow a better understanding of the processes involved in the formation of the universe. To cover these diverse areas, it is necessary to study different observables and collision systems. A particular challenge is to find a suitable measurable observable for a theoretically meaningful variable and to develop a measurement process taking into account the experiment. The analyses of particle collisions in this thesis cover many of the challenges and objectives mentioned above. The focus of the work is the analysis of isolated photons at an energy of √s = 7 TeV. In addition, the work also includes measurements of the average transverse momentum in Pb-Pb collisions at an energy of √s = 2.76 TeV.
Apart from the collision system, the two analyses complement each other in other respects. The measurement of isolated photons represents the first measurement of this observable with ALICE and thus lays the foundation for further measurements at other collision systems and energies. The measurement of the mean transverse momentum, on the other hand, is based on an established measurement and thus allows the comparison of different collision systems. Likewise, the physical processes studied differ. With the measurement of isolated photons, hard scattering processes in the collisions can be investigated, while the average transverse momentum allows a description of the underlying event.
When measuring isolated photons, it should be noted that isolated photons are a measurable observable that cannot be assigned to an explicit physical process. The isolation criterion used in the analysis serves to increase the fraction of prompt photons from 2→2 processes. These photons can contribute to a better understanding of the parton density function (PDF) of gluons, as well as be used as a reference for perturbative QCD calculations.
Of particular importance for the analysis are the cluster shape and the energy within a certain radius around the potential photon. The combination of these two quantities allows determining the background using the ABCD method established by CDF and ATLAS. The result obtained in this way extends the previous measurements of the cross-section of isolated photons at the LHC to lower transverse momenta. Similarly, the previous measurements of the cross-section as a function of the scale variable xT are extended to lower values.
The main focus of the measurement of the average transverse momentum of charged particles ⟨pT⟩ is to compare the measurement for the pp, p-Pb, and Pb-Pb collision systems. To obtain a direct comparison between the different collision systems, ⟨pT ⟩ is measured against the true multiplicity nch. Since the multiplicity range of pp and p-Pb collisions is limited, the analysis in Pb-Pb collisions is restricted to nch = 100. This range corresponds to peripheral Pb-Pb collisions. A particular focus of the analysis is the determination and reduction of the electromagnetic background in peripheral Pb-Pb collisions and the determination of nch based on the measured multiplicity nacc . The different collision systems show similar behavior with increasing multiplicity. The steepest increase occurs at low multiplicities and changes for all collision systems at nch = 14. With higher multiplicities, the slope reduces further, with the effect being most pronounced in Pb-Pb collisions.
This dissertation describes the development of the beam dynamics design of a novel superconducting linear accelerator. At a main operating frequency of 216.816 MHz, ions with a mass-to-charge ratio of up to 6 can be accelerated at high duty cycles up to CW operation. Intended for construction at the GSI Helmholtz Centre for Heavy Ion Research in Darmstadt, the focus of the work is on the beam dynamic design of the accelerator section downstream of the high charge injector (HLI) at an injection energy of 1.39 MeV/u. An essential feature of this linear accelerator (Linac) is the use of the EQUUS (Equidistant Multigap Structure) beam dynamics concept for a variably adjustable output energy between 3.5 and 7.3 MeV/u (corresponding to about 12.4 % of the speed of light) with a required low energy spread of maximum 3 keV/u.
The GSI Helmholtz Centre for Heavy Ion Research is a large-scale research facility that uses its particle accelerators to perform basic research with ion beams. Research on super-heavy elements ("SHE") is a major focus. It is expected that their production and research will provide answers to a large number of scientific questions. The production and detection of elements with atomic numbers 107 to 112 (Bohrium, Hassium, Meitnerium, Darmstadtium, Röntgenium and Copernicium) was first achieved at GSI between 1981 and 1996.
Key to this remarkable progress in SHE research were continuous developments and technical innovations. On the one hand, in the field of experimental sensitivity and detection of the nuclear reaction products and, on the other hand, in the field of accelerator technology.
For the acceleration of the projectile beam, the UNILAC (Universal Linear Accelerator), which was put into operation in 1975, has been used at GSI so far. In the course of the reconstruction and expansion of the research infrastructure at GSI, a dedicated new particle accelerator, HELIAC (Helmholtz Linear Accelerator), is now under development to meet the special requirements of the beam parameters for the synthesis of new superheavy elements. Typically, the production rates of super-heavy elements with effective cross sections in the picobarn range are very low. Therefore, a high duty cycle (up to CW operation) is a key feature of HELIAC. Thus, the required beam time for the desired nuclear reactions can be significantly shortened.
Theoretical preliminary work by Minaev et al. and newly created knowledge about design, fabrication, and operation of superconducting drift tube cavities have laid the foundation for this work and thus the development of the HELIAC linear accelerator. It consists of a superconducting and a normal conducting part. Acceleration takes place in the superconducting part in four cryomodules, each about 5 m long. These contain three CH cavities, one buncher cavity, two solenoid magnets for transverse beam focusing, and two beam position monitors (BPMs).
The following 10 m long normal conducting part is primarily used for beam transport and ends with a buncher cavity. This is operated at a halved frequency of 108.408 MHz.
A key feature of this accelerator is the variability of the output energy from 3.5 to 7.3 MeV/u with a small energy uncertainty of ±3 keV/u maximum over the entire output energy range. For the development of HELIAC, the EQUUS beam dynamics concept used combined the advantages of conventional linac designs with the high acceleration gradients of superconducting CH-DTLs. By doubling the frequency (compared to the GSI high charge injector) to 216.816 MHz in the superconducting section and using CH cavities at an acceleration gradient of maximum 7.1 MV/m, an acceleration efficiency with superconducting drift tube structures that is unique in the world is made possible. At the same time, the compact lengths of the CH cavities ensure good handling for both production and operation. EQUUS leads to longitudinal beam stability in all energy ranges of the accelerator with the sliding motion of the synchronous phase within each CH cavity. The rms emittance growth is moderate in all levels. The modular design of the HELIAC with four cryomodules basically allows the Linac to be commissioned starting with the first cryomodule, the so-called Advanced Demonstrator. In the subsequent expansion stage with only the first two cryomodules of HELIAC, the lower limit of the energy range to be provided by HELIAC (3.5 MeV/u) can already be clearly exceeded, so that use in regular beam operation at GSI is already conceivable from here on.
By means of error tolerance studies, the stability of the HELIAC beam dynamics design against possible alignment errors of the magnetic focusing elements and accelerator cavities as well as errors of the electric field amplitudes and phases have been investigated, basically confirmed and critical parameters have been determined. An additional steering concept via dipole correction coils at the solenoid magnets allows transverse beam control as well as diagnostics by means of two BPMs per cryomodule.
With completion of this work in 2021, the CH1 and CH2 cavities have already been built and are in the final preparation and cold test phase. In parallel, the development of the CH cavities CH3-11 has also been started.
The topic of this thesis is the theoretical description of the hadron gas stages in heavy-ion collisions. The overall addressed question hereby is: How does the hadronic medium evolve i.e. what are the relevant microscopic reaction mechanisms and the properties of the involved degrees of freedom? The main goal is to address this question specifically for hadronic multi-particle interactions. For this goal, the hadronic transport approach SMASH is extended with stochastic rates, which allow to include detailed balance fulfilling multi-particle reactions in the approach. Three types of reactions are newly-accounted for: 3-to-1, 3-to-2 and 5-to-2 reactions. After extensive verifications of the stochastic rates approach, they are used to study the effect of multi-particle interactions, particularly in afterburner calculations.
These studies follow complementary results for the dilepton and strangeness production with only binary reactions, which show that hadronic transport approaches are capable of describing observables when employed for the entire evolution of low-energy heavy-ion collisions. This is illustrated by the agreement of dilepton and strangeness production for smaller systems with SMASH calculations. It is, in particular, possible to match the measured strangeness production of phi and Xi hadrons via additional heavy nucleon resonance decay channels. For larger systems or higher energies, hadronic transport cascade calculations with vacuum resonance properties can point to medium effects. This is demonstrated extensively for the dilepton emission in comparisons to the full set of HADES dielectron data. The dilepton invariant mass spectra are sensitive to a medium modification of the vector meson spectral function for large collision systems already at low beam energies. The sensitivity to medium modifications is mapped out in detail by comparisons to a coarse-graining approach, which employs medium-modified spectral functions and is based on the same evolution.
The theoretical foundation of stochastic rates are collision probabilities derived from the Boltzmann equation's collision term with the assumption of a constant matrix element. This derivation is presented in a comprehensive and pedagogical fashion. The derived collision probabilities are employed for a stochastic collision criterion and various detailed-balance fulfilling multi-particle reactions: the mesonic Dalitz decay back-reaction (3-to-1), the deuteron catalysis (3-to-2) and the proton-antiproton annihilation back-reaction (5-to-2). The introduced stochastic rates approach is extensively verified by studies of the numerical stability and comparisons to previous results and analytic expectations. The stochastic rates results agree perfectly with the respective analytic results.
Physically, multi-particle reactions are demonstrated to be significant for different observables, most notably the yield of the partaking particles, even in the late dilute stage of heavy-ion reactions. They lead to a faster equilibration of the system than equivalent binary multi-step treatments. The difference in equilibration consequently influences the yield in afterburner calculations. Interestingly, the interpretation of results is not dependent on employing multi-particle or multi-step treatments, which a posteriori validates the latter.
As the first test case of multi-particle reactions in heavy-ion reactions, the mesonic 3-to-1 Dalitz decay is found to be dominated by the omega Dalitz decay back-reaction. While the effect on the medium is found to be negligible overall, the regeneration is found to be sizable: up to a quarter of Dalitz decays are regenerated.
Non-equilibrium rescattering effects are shown to be relevant for late collision stages for two particle species: deuteron and protons. In both cases, the relevant rescatterings involve multiple particles.
The deuteron pion and nucleon catalysis reactions equilibrate quickly in the afterburner stage at intermediate energies. The constant formation and destruction keeps the yield constant and microscopically explains the "snowballs in hell"-paradox. The yield is also generated with no d present at early times, which explains why coalescence models can also match the multiplicity.
New is the study of the 5-body back-reaction of proton-antiproton annihilations. This work marks the first realization of microscopic 5-body reactions in a transport approach to fulfill detailed balance for such reactions. A sizable regeneration due to the back-reaction of up to half of the proton-antiproton pairs lost due to annihilations is found. Consequently, both annihilation and regeneration in the late non-equilibrium stage are shown to have a significant effect on the p yield.
This thesis deals with the phenomenology of QCD matter, its aspects in heavy ion collisions and in neutron stars. The first half of the work focuses on the hadronic phase of QCD matter. One focus is on how the hadronic phase shows itself in heavy ion collisions and how its dynamics can be simulated. The role of hadronic interactions is considered in the context of the lattice QCD data. The second part of this thesis presents a unified approach to QCD matter, the CMF model. The CMF model incorporates many aspects of QCD phenomenology which allows for a consistent description of the hadron-quark transition, making it applicable to the entire QCD phase diagram, i.e., to the cold nuclear matter and to the hot QCD matter. It is shown that a description of both the hot matter created in heavy ion collisions and the cold dense matter in neutron star interiors is possible within one single approach, the CMF model.