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We report on the production of inclusive Υ(1S) and Υ(2S) in p-Pb collisions at sNN−−−√=5.02 TeV at the LHC. The measurement is performed with the ALICE detector at backward (−4.46<ycms<−2.96) and forward (2.03<ycms<3.53) rapidity down to zero transverse momentum. The production cross sections of the Υ(1S) and Υ(2S) are presented, as well as the nuclear modification factor and the ratio of the forward to backward yields of Υ(1S). A suppression of the inclusive Υ(1S) yield in p-Pb collisions with respect to the yield from pp collisions scaled by the number of binary nucleon-nucleon collisions is observed at forward rapidity but not at backward rapidity. The results are compared to theoretical model calculations including nuclear shadowing or partonic energy loss effects.
Transverse momentum spectra of π±, K± and p(p¯) up to pT = 20 GeV/c at mid-rapidity in pp and Pb-Pb collisions at sNN−−−√= 2.76 TeV have been measured using the ALICE detector at the Large Hadron Collider. The proton-to-pion and the kaon-to-pion ratios both show a distinct peak at pT≈3GeV/c in central Pb-Pb collisions. Below the peak, pT < 3 GeV/c, both ratios are in good agreement with hydrodynamical calculations, suggesting that the peak itself is dominantly the result of radial flow rather than anomalous hadronization processes. For pT > 10 GeV/c particle ratios in pp and Pb-Pb collisions are in agreement and the nuclear modification factors for π±, K± and p(p¯) indicate that, within the systematic and statistical uncertainties, the suppression is the same. This suggests that the chemical composition of leading particles from jets in the medium is similar to that of vacuum jets.
The colour-singlet axial-vector vertex plays a pivotal role in understanding dynamical chiral symmetry breaking and numerous hadronic weak interactions, yet scant model-independent information is available. We therefore use longitudinal and transverse Ward–Green–Takahashi (WGT) identities, together with kinematic constraints, in order to ameliorate this situation and expose novel features of the axial vertex: amongst them, Ward-like identities for elements in the transverse piece of the vertex, which complement and shed new light on identities determined previously for components in its longitudinal part. Such algebraic results are verified via solutions of the Bethe–Salpeter equation for the axial vertex obtained using two materially different kernels for the relevant Dyson–Schwinger equations. The solutions also provide insights that suggest a practical Ansatz for the axial-vector vertex.
We explore the parameter space of the two-flavor thermal quark–meson model and its Polyakov loop-extended version under the influence of a constant external magnetic field B. We investigate the behavior of the pseudo critical temperature for chiral symmetry breaking taking into account the likely dependence of two parameters on the magnetic field: the Yukawa quark–meson coupling and the parameter T0 of the Polyakov loop potential. Under the constraints that magnetic catalysis is realized at zero temperature and the chiral transition at B=0 is a crossover, we find that the quark–meson model leads to thermal magnetic catalysis for the whole allowed parameter space, in contrast to the present picture stemming from lattice QCD.
Coherent photo-production of sons in ultra-peripheral Pb-Pb collisions at the LHC measured by ALICE
(2014)
We present the differential cross section for coherent ρ0 photo-production at mid-rapidity (−0.5 < y < 0.5) measured by the ALICE experiment in Pb-Pb collisions at √sNN = 2.76 TeV at the LHC, as well as the total ρ0 cross section obtained by modelbased extrapolation to all rapidities. These cross sections are compared to various model predictions, as well as to earlier measurements at RHIC. In addition, we present results on nuclear breakup in coincidence with coherent ρ0 photo-production.
We study vacuum masses of charmonia and the charm-quark diffusion coefficient in the quark-gluon plasma based on the spectral representation for meson correlators. To calculate the correlators, we solve the quark gap equation and the inhomogeneous Bethe–Salpeter equation in the rainbow-ladder approximation. It is found that the ground-state masses of charmonia in the pseudoscalar, scalar, and vector channels can be well described. For 1.5Tc<T<3.0Tc, the value of the diffusion coefficient D is comparable with that obtained by lattice QCD and experiments: 3.4<2πTD<5.9. Relating the diffusion coefficient with the ratio of shear viscosity to entropy density η/s of the quark-gluon plasma, we obtain values in the range 0.09<η/s<0.16.
We present a simultaneous calculation of heavy single-Λ hypernuclei and compact stars containing hypernuclear core within a relativistic density functional theory based on a Lagrangian which includes the hyperon octet and lightest isoscalar-isovector mesons which couple to baryons with density-dependent couplings. The corresponding density functional allows for SU(6) symmetry breaking and mixing in the isoscalar sector, whereby the departures in the σ–Λ and σ–Σ couplings away from their values implied by the SU(3) symmetric model are used to adjust the theory to the laboratory and astronomical data. We fix σ–Λ coupling using the data on the single-Λ hypernuclei and derive an upper bound on the σ–Σ from the requirement that the lower bound on the maximum mass of a compact star is 2M⊙.
In this work the baryon number and strange susceptibility of second and fourth order are presented. The results at zero baryon-chemical potential are obtained using a well tested chiral effective model including all known hadron degrees of freedom and additionally implementing quarks and gluons in a PNJL-like approach. Quark and baryon number susceptibilities are sensitive to the fundamental degrees of freedom in the model and signal the shift from massive hadrons to light quarks at the deconfinement transition by a sharp rise at the critical temperature. Furthermore, all susceptibilities are found to be largely suppressed by repulsive vector field interactions of the particles. In the hadronic sector vector repulsion of baryon resonances restrains fluctuations to a large amount and in the quark sector above Tc even small vector field interactions of quarks quench all fluctuations unreasonably strong. For this reason, vector field interactions for quarks have to vanish in the deconfinement limit.
We show how repulsive interactions of deconfined quarks as well as confined hadrons have an influence on the baryon number susceptibilities and the curvature of the chiral pseudo-critical line in effective models of QCD. We discuss implications and constraints for the vector interaction strength from comparisons to lattice QCD and comment on earlier constraints, extracted from the curvature of the transition line of QCD and compact star observables. Our results clearly point to a strong vector repulsion in the hadronic phase and near-zero repulsion in the deconfined phase.
We study the phase structure of QCD at finite temperature within a Polyakov-loop extended quark–meson model. Such a model describes the chiral as well as the confinement-deconfinement dynamics. In the present investigation, based on the approach and results put forward in [1], [2], [3], [4], both matter and glue fluctuations are included. We present results for the order parameters as well as some thermodynamic observables and find very good agreement with recent results from lattice QCD.
Within the statistical model, the net strangeness conservation and incomplete total strangeness equilibration lead to the suppression of strange particle multiplicities. Furthermore, suppression effects appear to be stronger in small systems. By treating the production of strangeness within the canonical ensemble formulation we developed a simple model which allows to predict the excitation function of K+/π+ ratio in nucleus–nucleus collisions. In doing so we assumed that different values of K+/π+, measured in p + p and Pb + Pb interactions at the same collision energy per nucleon, are driven by the finite size effects only. These predictions may serve as a baseline for experimental results from NA61/SHINE at the CERN SPS and the future CBM experiment at FAIR.
The fluctuations in the ideal quantum gases are studied using the strongly intensive measures Δ[A,B] and Σ[A,B] defined in terms of two extensive quantities A and B. In the present Letter, these extensive quantities are taken as the motional variable, A=X, the system energy E or transverse momentum PT, and number of particles, B=N. This choice is most often considered in studying the event-by-event fluctuations and correlations in high energy nucleus–nucleus collisions. The recently proposed special normalization ensures that Δ and Σ are dimensionless and equal to unity for fluctuations given by the independent particle model. In statistical mechanics, the grand canonical ensemble formulation within the Boltzmann approximation gives an example of independent particle model. Our results demonstrate the effects due to the Bose and Fermi statistics. Estimates of the effects of quantum statistics in the hadron gas at temperatures and chemical potentials typical for thermal models of hadron production in high energy collisions are presented. In the case of massless particles and zero chemical potential the Δ and Σ measures are calculated analytically.
The electric dipole strength distribution in 130Te has been investigated using the method of Nuclear Resonance Fluorescence. The experiments were performed at the Darmstadt High Intensity Photon Setup using bremsstrahlung as photon source and at the High Intensity -Ray Source, where quasi-monochromatic and polarized photon beams are provided. Average decay properties of 130Te below the neutron separation energy are determined. Comparing the experimental data to the predictions of the statistical model indicate, that nuclear structure effects play an important role even at sufficiently high excitation energies. Preliminary results will be presented.
Fission fragment mass distributions were measured in heavy-ion induced fissions using 238U target nucleus. The measured mass distributions changed drastically with incident energy. The results are explained by a change of the ratio between fusion and qasifission with nuclear orientation. A calculation based on a fluctuation dissipation model reproduced the mass distributions and their incident energy dependence. Fusion probability was determined in the analysis, and the values were consistent with those determined from the evaporation residue cross sections.
The Facility for Antiproton and Ion Research (FAIR), under construction at Darmstadt will provide intense relativistic beams of exotic nuclei at its Superconducting-FRagment Separator. High-resolution in-beam γ-ray spectroscopy will be performed in the HISPEC experiment, using the European Advanced GAmma-ray Tracking Array (AGATA). The PreSPEC-AGATA campaign is the predecessor of HISPEC and runs from 2012 to 2014 at GSI Helmholtzzentrum für Schwerionenforschung GmbH. Up to19 AGATA modules were used at GSI's F Ragment Separator in 2012. We report on the status of the experiment including preliminary results from performance commissioning.
The n_TOF facility operates at CERN with the aim of addressing the request of high accuracy nuclear data for advanced nuclear energy systems as well as for nuclear astrophysics. Thanks to the features of the neutron beam, important results have been obtained on neutron induced fission and capture cross sections of U, Pu and minor actinides. Recently the construction of another beam line has started; the new line will be complementary to the first one, allowing to further extend the experimental program foreseen for next measurement campaigns.
The production of charmonia in the antiproton-nucleus reactions at plab = 3 − 10 GeV/c is studied within the Glauber model and the generalized eikonal approximation. The main reaction channel is charmonium formation in an antiproton-proton collision. The target mass dependence of the charmonium transparency ratio allows to determine the charmonium-nucleon cross section. The polarization effects in the production of χc2 states are evaluated.
The simultaneous description of the hadronic yields, pion, kaon and proton spectra, elliptic flows and femtoscopy scales in hydrokinetic model of A+A collisions is presented at different centralities for the top RHIC and LHC energies. The hydrokinetic model is used in its hybrid version that allows one to switch correctly to the UrQMD cascade at the isochronic hypersurface which separates the cascade stage and decaying hydrodynamic one. The results are compared with pure hybrid model where hydrodynamics and hadronic cascade are matching just at the non-space-like hypersurface of chemical freeze-out. The initial conditions are based on both Glauber- and KLN- Monte-Carlo simulations and results are compared. It seems that the observables, especially femtoscopy data, prefer the Glauber initial conditions. The modification of the particle number ratios caused, in particular, by the particle annihilations at the afterburn stage is analyzed.
The HADES collaboration has searched for the anti-kaonic nuclear cluster “ppK−” in p+p collisions by its decay into pΛ. In the course of this analysis several cross checks had to be performed. This report discusses two examples thereof. In one test it was checked whether the presence of background events could introduce a bias on the applied partial wave analysis. The second item discussed here is the extraction of the total pK+Λ production cross section necessary to derive the absolute upper limit on the “ppK−” production cross section.
The study of neutron-induced reactions is of high relevance in a wide variety of fields, ranging from stellar nucleosynthesis and fundamental nuclear physics to applications of nuclear technology. In nuclear energy, high accuracy neutron data are needed for the development of Generation IV fast reactors and accelerator driven systems, these last aimed specifically at nuclear waste incineration, as well as for research on innovative fuel cycles. In this context, a high luminosity Neutron Time Of Flight facility, n_TOF, is operating at CERN since more than a decade, with the aim of providing new, high accuracy and high resolution neutron cross-sections. Thanks to the features of the neutron beam, a rich experimental program relevant to nuclear technology has been carried out so far. The program will be further expanded in the near future, thanks in particular to a new high-flux experimental area, now under construction.
We propose an effective theory of SU(3) gluonic matter where interactions between color-electric and color-magnetic gluons are constrained by the center and scale symmetries. Through matching to the dimensionally-reduced magnetic theories, the magnetic gluon condensate qualitatively changes its thermal behavior above the critical temperature. We argue its phenomenological consequences for the thermodynamics, in particular the dynamical breaking of scale invariance.
The so-called Pygmy Dipole Resonance, an additional structure of low-lying electric dipole strength, has attracted strong interest in the last years. Different experimental approaches have been used in the last decade in order to investigate this new interesting nuclear excitation mode. In this contribution an overview on the available experimental data is given.
Many QCD based and phenomenological models predict changes of hadron properties in a strongly interacting environment. The results of these models differ significantly and the experimental determination of hadron properties in nuclear matter is essential. In this paper we present a review of selected physics results obtained at GSI Helmholtzzentrum für Schwerionenforschung GmbH by HADES (High-Acceptance Di-Electron Spectrometer). The e+e− pair emission measured for proton and heavy-ion induced collisions is reported together with results on strangeness production. The future HADES activities at the planned FAIR facility are also discussed.
The High Acceptance DiElectron Spectrometer HADES [1] is installed at the Helmholtzzentrum für Schwerionenforschung (GSI) accelerator facility in Darmstadt. It investigates dielectron emission and strangeness production in the 1-3 AGeV regime. A recent experiment series focusses on medium-modifications of light vector mesons in cold nuclear matter. In two runs, p+p and p+Nb reactions were investigated at 3.5 GeV beam energy; about 9·109 events have been registered. In contrast to other experiments the high acceptance of the HADES allows for a detailed analysis of electron pairs with low momenta relative to nuclear matter, where modifications of the spectral functions of vector mesons are predicted to be most prominent. Comparing these low momentum electron pairs to the reference measurement in the elementary p+p reaction, we find in fact a strong modification of the spectral distribution in the whole vector meson region.
We review recent results on J/ψ production measured by the ALICE collaboration at the LHC. For pp collisions at √s = 7 TeV yields and spectra of inclusive and prompt J/ψ, as well as results on their polarization and the charged particle multiplicity dependence of yields are presented. Measurements of the nuclear modification factor RAA of inclusive J/ψ at mid-(|y| < 0.9) and forward-rapidities (2.5 < y < 4), covering the range to pt = 0, for centrality selected Pb-Pb collisions are discussed. Also, first results on the J/ψυ2 at forward-rapidities are shown.
During the 2011 Pb-Pb run, dedicated triggers were used by the ALICE Collaboration to enrich ultra-peripheral collisions (UPC) to measure the J/ψ production cross section and its rapidity dependence at a centre of mass energy of 2.76 TeV per nucleon pair. In this article, the ongoing studies on J/ψ photoproduction in UPC events are presented.
The neutron sensitivity of the C6D6 detector setup used at n_TOF facility for capture measurements has been studied by means of detailed GEANT4 simulations. A realistic software replica of the entire n_TOF experimental hall, including the neutron beam line, sample, detector supports and the walls of the experimental area has been implemented in the simulations. The simulations have been analyzed in the same manner as experimental data, in particular by applying the Pulse Height Weighting Technique. The simulations have been validated against a measurement of the neutron background performed with a natC sample, showing an excellent agreement above 1 keV. At lower energies, an additional component in the measured natC yield has been discovered, which prevents the use of natC data for neutron background estimates at neutron energies below a few hundred eV. The origin and time structure of the neutron background have been derived from the simulations. Examples of the neutron background for two different samples are demonstrating the important role of accurate simulations of the neutron background in capture cross-section measurements.
We report on the measurement of the inclusive Υ (1S) production in Pb–Pb collisions at √sNN = 2.76 TeV carried out at forward rapidity (2.5 < y < 4) and down to zero transverse momentum using its μ+μ−decay channel with the ALICE detector at the Large Hadron Collider. A strong suppression of the inclusive Υ (1S) yield is observed with respect to pp collisions scaled by the number of independent nucleon–nucleon collisions. The nuclear modification factor, for events in the 0–90% centrality range, amounts to 0.30 ± 0.05(stat) ± 0.04(syst). The observed Υ (1S) suppression tends to increase with the centrality of the collision and seems more pronounced than in corresponding mid-rapidity measurements. Our results are compared with model calculations, which are found to underestimate the measured suppression and fail to reproduce its rapidity dependence.
Transverse momentum spectra of π±, K± and p(p¯) up to pT = 20 GeV/c at mid-rapidity in pp, peripheral (60–80%) and central (0–5%) Pb–Pb collisions at √sNN = 2.76 TeV have been measured using the ALICE detector at the Large Hadron Collider. The proton-to-pion and the kaon-to-pion ratios both show a distinct peak at pT ≈ 3 GeV/c in central Pb–Pb collisions. Below the peak, pT < 3 GeV/c, both ratios are in good agreement with hydrodynamical calculations, suggesting that the peak itself is dominantly the result of radial flow rather than anomalous hadronization processes. For pT > 10 GeV/c particle ratios in pp and Pb–Pb collisions are in agreement and the nuclear modification factors for π±, K± and p(p¯) indicate that, within the systematic and statistical uncertainties, the suppression is the same. This suggests that the chemical composition of leading particles from jets in the medium is similar to that of vacuum jets.
Freeze-out radii extracted from three-pion cumulants in pp, p–Pb and Pb–Pb collisions at the LHC
(2014)
In high-energy collisions, the spatio-temporal size of the particle production region can be measured using the Bose–Einstein correlations of identical bosons at low relative momentum. The source radii are typically extracted using two-pion correlations, and characterize the system at the last stage of interaction, called kinetic freeze-out. In low-multiplicity collisions, unlike in high-multiplicity collisions, two-pion correlations are substantially altered by background correlations, e.g. mini-jets. Such correlations can be suppressed using three-pion cumulant correlations. We present the first measurements of the size of the system at freeze-out extracted from three-pion cumulant correlations in pp, p–Pb and Pb–Pb collisions at the LHC with ALICE. At similar multiplicity, the invariant radii extracted in p–Pb collisions are found to be 5–15% larger than those in pp, while those in Pb–Pb are 35–55% larger than those in p–Pb. Our measurements disfavor models which incorporate substantially stronger collective expansion in p–Pb as compared to pp collisions at similar multiplicity.
We report on a polarization measurement of inclusive J/ψ mesons in the di-electron decay channel at mid-rapidity at 2 < pT < 6 GeV/c in p + p collisions at √s = 200 GeV. Data were taken with the STAR detector at RHIC. The J/ψ polarization measurement should help to distinguish between different models of the J/ψ production mechanism since they predict different pT dependences of the J/ψ polarization. In this analysis, J/ψ polarization is studied in the helicity frame. The polarization parameter λθ measured at RHIC becomes smaller towards high pT , indicating more longitudinal J/ψ polarization as pT increases. The result is compared with predictions of presently available models.
The ALICE Collaboration at the LHC reports measurement of the inclusive production cross section of electrons from semi-leptonic decays of beauty hadrons with rapidity |y| < 0.8 and transverse momentum 1 < pT < 10 GeV/c, in pp collisions at √s = 2.76 TeV. Electrons not originating from semi-electronic decay of beauty hadrons are suppressed using the impact parameter of the corresponding tracks. The production cross section of beauty decay electrons is compared to the result obtained with an alternative method which uses the distribution of the azimuthal angle between heavy-flavour decay electrons and charged hadrons. Perturbative QCD predictions agree with the measured cross section within the experimental and theoretical uncertainties. The integrated visible cross section, σb→e = 3.47 ± 0.40(stat) +1.12 −1.33(sys) ± 0.07(norm) μb, was extrapolated to full phase space using Fixed Order plus Next-to-Leading Log (FONLL) calculations to obtain the total bb production ¯ cross section, σbb¯ = 130 ± 15.1(stat) +42.1 −49.8(sys) +3.4 −3.1(extr) ± 2.5(norm) ± 4.4(BR) μb.
Weltweit arbeiten Astrophysiker noch immer mit einer Theorie, die bereits vor rund 100 Jahren aufgestellt wurde – die Einstein’sche Relativitätstheorie. Nahezu jeder hat den genialen Kopf dahinter vor Augen: Albert Einstein. Was aber ist der von Einstein prognostizierte gekrümmte Raum, was sind schwarze Löcher und Neutronensterne und wer sind die Menschen, die auf diesen Gebieten forschen? Luciano Rezzolla, seit Oktober 2013 Professor für Theoretische Astrophysik an der Goethe-Universität sowie Leiter einer Arbeitsgruppe am Max-Planck-Institut für Gravitationsphysik in Potsdam, ist einer dieser Forscher.
The ( J, T ) = (1, 1) parity doublet in 20Ne at 11.26 MeV is a good candidate to study parity violation in nuclei. However, its energy splitting is known with insufficient accuracy for quantitative estimates of parity violating effects. To improve on this unsatisfactory situation, nuclear resonance fluorescence experiments using linearly and circularly polarized γ -ray beams were used to determine the energy difference of the parity doublet E = E(1−) − E(1+) = −3.2(±0.7)stat( +0.6 −1.2)sys keV and the ratio of their integrated cross sections I (+) s,0 /I (−) s,0 = 29(±3)stat( +14 −7 )sys. Shell-model calculations predict a parityviolating matrix element having a value in the range 0.46–0.83 eV for the parity doublet. The small energy difference of the parity doublet makes 20Ne an excellent candidate to study parity violation in nuclear excitations.
In this paper we discuss to what extent one can infer details of the interior structure of a black hole based on its horizon. Recalling that black hole thermal properties are connected to the non-classical nature of gravity, we circumvent the restrictions of the no-hair theorem by postulating that the black hole interior is singularity free due to violations of the usual energy conditions. Further these conditions allow one to establish a one-to-one, holographic projection between Planckian areal “bits” on the horizon and “voxels”, representing the gravitational degrees of freedom in the black hole interior. We illustrate the repercussions of this idea by discussing an example of the black hole interior consisting of a de Sitter core postulated to arise from the local graviton quantum vacuum energy. It is shown that the black hole entropy can emerge as the statistical entropy of a gas of voxels.
Top-down influences on ambiguous perception: the role of stable and transient states of the observer
(2014)
The world as it appears to the viewer is the result of a complex process of inference performed by the brain. The validity of this apparently counter-intuitive assertion becomes evident whenever we face noisy, feeble or ambiguous visual stimulation: in these conditions, the state of the observer may play a decisive role in determining what is currently perceived. On this background, ambiguous perception and its amenability to top-down influences can be employed as an empirical paradigm to explore the principles of perception. Here we offer an overview of both classical and recent contributions on how stable and transient states of the observer can impact ambiguous perception. As to the influence of the stable states of the observer, we show that what is currently perceived can be influenced (1) by cognitive and affective aspects, such as meaning, prior knowledge, motivation, and emotional content and (2) by individual differences, such as gender, handedness, genetic inheritance, clinical conditions, and personality traits and by (3) learning and conditioning. As to the impact of transient states of the observer, we outline the effects of (4) attention and (5) voluntary control, which have attracted much empirical work along the history of ambiguous perception. In the huge literature on the topic we trace a difference between the observer's ability to control dominance (i.e., the maintenance of a specific percept in visual awareness) and reversal rate (i.e., the switching between two alternative percepts). Other transient states of the observer that have more recently drawn researchers' attention regard (6) the effects of imagery and visual working memory. (7) Furthermore, we describe the transient effects of prior history of perceptual dominance. (8) Finally, we address the currently available computational models of ambiguous perception and how they can take into account the crucial share played by the state of the observer in perceiving ambiguous displays.
Physics at its core is an experimental pursuit. If one theory does not agree with experimental results, then the theory is wrong. However, it is becoming harder and harder to directly test some theories of fundamental physics at the high energy/small distance frontier exactly because this frontier is becoming technologically harder to reach. The Large Hadron Collider is getting near the limit of what we can do with present accelerator technology in terms of directly reaching the energy frontier. The motivation for this special issue was to try and collect together ideas and potential approaches to experimentally probe some of our ideas about physics at the high energy/small distance frontier. Some of the papers in this special issue directly deal with the issue of what happens to spacetime at small distance scales. In the paper by A. Aurilia and E. Spallucci a picture of quantum spacetime is given based on the effects of ultrahigh velocity length contractions on the structure of the spacetime. The work of P. Nicolini et al. further pursues the idea that spacetime has a minimal length. The consequences of this minimal length are investigated in terms of the effects it would have on the gravitational collapse of a star to form a black hole. In the article by G. Amelino-Camelia et al. the quantum structure of spacetime is studied through the Fermi LAT data on the Gamma Ray Burst GRB130427A. The article by S. Hossenfelder addressed the question of whether spacetime is fundamentally continuous or discrete and postulates that in the case when spacetime is discrete it might have defects which would have important observational consequences. ...
This paper studies the geometry and the thermodynamics of a holographic screen in the framework of the ultraviolet self-complete quantum gravity. To achieve this goal we construct a new static, neutral, nonrotating black hole metric, whose outer (event) horizon coincides with the surface of the screen. The spacetime admits an extremal configuration corresponding to the minimal holographic screen and having both mass and radius equalling the Planck units. We identify this object as the spacetime fundamental building block, whose interior is physically unaccessible and cannot be probed even during the Hawking evaporation terminal phase. In agreement with the holographic principle, relevant processes take place on the screen surface. The area quantization leads to a discrete mass spectrum. An analysis of the entropy shows that the minimal holographic screen can store only one byte of information, while in the thermodynamic limit the area law is corrected by a logarithmic term.
The Generalized Uncertainty Principle (GUP) arises from Quantum Gravity thought experiments and contains a minimal lenght. In this thesis I calculate Schwarzschild Black Holes that are modified by the GUP. These Black Holes have the property, that their temperature does not diverge for small masses, although they still posses a curvature singularity. I calculate analytically that in more than 3+1 dimensions the temperature diverges again.
In this thesis, Planck size black holes are discussed. Specifically, new families of black holes are presented. Such black holes exhibit an improved short scale behaviour and can be used to implement gravity self-complete paradigm. Such geometries are also studied within the ADD large extra dimensional scenario. This allows black hole remnant masses to reach the TeV scale. It is shown that the evaporation endpoint for this class of black holes is a cold stable remnant. One family of black holes considered in this thesis features a regular de Sitter core that counters gravitational collapse with a quantum outward pressure. The other family of black holes turns out to nicely fit into the holographic information bound on black holes, and lead to black hole area quantization and applications in the gravitational entropic force. As a result, gravity can be derived as emergent phenomenon from thermodynamics.
The thesis contains an overview about recent quantum gravity black hole approaches and concludes with the derivation of nonlocal operators that modify the Einstein equations to ultraviolet complete field equations.
The radiative capture cross section of 238U is very important for the developing of new reactor technologies and the safety of existing ones. Here the preliminary results of the 238U(n,γ) cross section measurement performed at n_TOF with C6D6 scintillation detectors are presented, paying particular attention to data reduction and background subtraction.
Electromagnetic calorimeter (ECAL) is being developed to complement dilepton spectrometer HADES. ECAL will enable the HADES@FAIR experiment to measure data on neutral meson production in heavy ion collisions at the energy range of 2-10 AGeV on the beam of future accelerator SIS100@FAIR. We will report results of the last beam test with quasi-monoenergetic photons carried out in MAMI facility at Johannes Gutenberg Universität Mainz.
The quark gluon plasma produced in heavy ion collisions behaves like an almost ideal fluid described by viscous hydrodynamics with a number of transport coefficients. The second order coefficient κ is related to a Euclidean correlator of the energy-momentum tensor at vanishing frequency and low momentum. This allows for a lattice determination without maximum entropy methods or modelling, but the required lattice sizes represent a formidable challenge. We calculate κ in leading order lattice perturbation theory and simulations on 1203 × 6, 8 lattices with a < 0.1 fm. In the temperature range 2Tc − 10Tc we find κ = 0.36(15)T2. The error covers both a suitably rescaled AdS/CFT prediction as well as, remarkably, the result of leading order perturbation theory. This suggests that appropriate noise reduction methods on the lattice and NLO perturbative calculations could provide an accurate QCD prediction in the near future.
Ultrafast protein dynamics are of great interest for understanding the molecular basis of biochemical function. One method to study structural changes with highest time-resolution starting in the femtosecond regime is 2D-IR spectroscopy. However its application to investigate protein dynamics both with high temporal and spatial resolution is currently limited to few biological systems with intrinsic chromophores. Spectral congestion, the contribution of many similar oscillators to the same signals, makes it difficult to draw conclusions about local structural dynamics in most other proteins.
The aim of this thesis is to extend the application of 2D-IR spectroscopy to a wider range of proteins by introducing unnatural amino acids (UAAs) with azide or nitrile groups as site-specific vibrational probes, which absorb in the free spectral window between 1800 to 3000 cm-1 by using methods from chemical biology.
In a comparative experimental study using FTIR and 2D-IR spectroscopy of single amino acids azidohomoalanine (Aha), a methionine analogue, was identified as preferred label. To demonstrate the application potential of UAAs as site-specific probes, Aha was then incorporated into different positions in a small globular protein. By using both FTIR and ultrafast 2D-IR it was shown, that indeed the local microenvironment as well as conformational fluctuations on picosecond timescale could be monitored with high spatial information. The azide moiety shows a shift of its absorption frequency depending on the polarity of its surrounding. Using this approach, different subensembles for the protein conformations with more polar and less polar environment around the vibrational probe can be distinguished.
A second major application of site-specific labels is the study of vibrational energy transfer processes (VET), predicted to be relevant for allosteric communication in protein domains such as the PDZ domain. VET can be tracked with high spatial resolution using time-resolved IR spectroscopy by exciting a localized vibrational mode and probing separate modes in a two-colour 2D-IR experiment. To extend this kind of experiment to proteins, a specific donor-acceptor pair of two UAAs was introduced. It uses an azulene moiety as donor that can be excited in the visible range but deposits the excess energy by internal conversion into the vibrational modes of the ground state. In small peptides this VET pair was applied successfully, showing a distance-dependent energy transfer induced signal for VET through covalent bonds. These findings bare great promise for the direct observation of vibrational energy flow in proteins in real-time.
Overall this thesis is the basis for extending the usability of 2D-IR spectroscopy to study structural dynamics in a wide range of proteins systems both with high temporal and spatial resolution.
The measurement of dielectrons (electron-positron pairs) allows to investigate the properties of strongly interacting matter, in particular the Quark-Gluon Plasma (QGP), which is created in relativistic heavy-ion collisions at the LHC. The evolution of the collision can be probed via dielectrons since electrons do not interact strongly and are created during all stages of the collision. One of the interests in dielectron measurements is motivated by possible modifications of the electromagnetic emission spectrum in the QGP, where pp collisions are used as a medium-free reference. The dielectron spectrum consists of contributions from various processes. In order to estimate contributions of known dielectron sources, simulations of the so-called dielectron cocktail are performed. In this thesis, dielectron cocktails in minimum bias pp collisions at p s = 7 TeV, p–Pb collisions at p sNN = 5.02 TeV and in central (0-10%) and semi-central (20-50%) Pb–Pb collisions at p sNN = 2.76 TeV at the LHC are presented.
In dieser Arbeit wurde die Leistungsfähigkeit des neuen Inner Tracking System (ITS) in Bezug auf die Messung von Spektren der invarianten Masse von Dielektronpaaren im Rahmen des ALICE Experiments am LHC ausgewertet. Zu Beginn der Planungen zum zukünftigen ITS wurden zwei verschiedene Designmöglichkeiten in Betracht gezogen: Auf der einen Seite ein ITS, welches die Möglichkeit zur Teilchenidentifizierung mittels spezifischem Energieverlust pro Wegstrecke bietet und auf der anderen Seite ein ITS welches diese Möglichkeiten nicht hat. Es wurde untersucht, ob es zukünftig möglich sein wird aus der Steigung des Spektrums der invarianten Masse von Dileptonen zwischen 1,1 GeV/c2 < Mee < 2,0 GeV/c2 direkt die Temperatur des Quark-Gluon-Plasmas zu extrahieren. Weiterhin wurde geprüft welches der beiden Systeme diese Aufgabe besser erfüllt.
Das neue ITS bietet gegenüber dem alten ITS Vorteile, die in dieser Analyse genutzt wurden. Zuerst, siehe Abschnitt 3.4, wurde ein zweidimensionaler Schnitt auf den Öffnungswinkel und die invariante Masse angewandt um Elektronen und Positronen aus Dalitzzerfällen und Photonkonversionen zu identifizieren und für die folgende Analyse zu verwerfen. Hierzu wurde die verbesserte Spurfindungseffizienz hin zu kleinen Transversalimpulsen ausgenutzt, um die Anzahl an zu kombinierenden Teilchen und damit die Wahrscheinlichkeit richtige Paare zu finden, zu erhöhen. Allerdings können Teilchen, welche nur im ITS nachgewiesen werden können, nicht zweifelsfrei (ITSPID), beziehungsweise gar nicht (ITSnoPID) identifiziert werden. Die Simulationen ergeben, dass ein zukünftiges ITS mit der Möglichkeit zur Teilchenidentifizierung leicht bessere Werte in der Signifikanz und im Verhältnis von Signal zu Untergrund liefern kann.
Die verbesserte Vertexfindung wird zur Reduktion des Beitrags durch Elektronen und Positronen aus semileptonisch zerfallenden D-Mesonen (Abschnitt 3.4.4) ausgenutzt.
Die Elektronen und Positronen, welche nach den Schnitten in der Stichprobe blieben, wurden verwendet um den Untergrund zu simulieren (Abschnitt 3.4.5). Daraufhin wurde die Signifikanz und das Verhältnis von Signal zu Untergrund berechnet. Mit diesen Informationen (Abschnitt 3.5.3) wurde ein Spektrum der invarianten Masse von Dileptonen mit der zu erwartenden Anzahl von 2,5 · 109 zentralen Blei-Blei-Kollisionen erzeugt. Dies führt zu den in Abschnitt 3.5.4 gezeigten Spektren. Nach Abzug der Beiträge durch die semileptonischen D-Meson Zerfälle und durch den hadronischen Cocktail ist noch der zu erwartende Beitrag durch die thermische Strahlung (Abschnitt 1.5) im Spektrum vorhanden. Eine Parametrisierung dieser Kurve ergibt die Temperatur des Quark-Gluon-Plasmas.
Der Unterschied der ermittelten Messwerte der Temperatur zwischen dem zukünftigen ITS mit Teilchenidentifizierung und ohne ist gering (Abschnitt 3.5.5). Die Messung ergibt keine signifikanten Unterschiede zwischen beiden ITS Entwürfen. Aufgrund dieses Ergebnisses kann man sagen, dass für die Messung von Dileptonen im Niedrigmassenbereich keine ITS PID notwendig ist. In den mittlerweile veröffentlichten ITS Technical Design Report sind die Ergebnisse dieser Studie eingeflossen. Es wurde beschlossen, dass der ITSnoPID umgesetzt wird.
Da in der Run 3 Periode des CERN LHC die Kollisionsrate auf 50 kHz erhöht werden soll, muss die ALICE TPC umgebaut werden. Die Vieldrahtproportionalkammern mit Sperrgitter sollen gegen eine GEM-basierte Auslese ausgetauscht werden, um eine kontinuierliche Auslese zu ermöglichen.
Es wurde eine GEM-Testkammer, die mit drei und vier GEM-Folien betrieben werden kann, entwickelt und gebaut. GEM-Folien wurden unter dem Mikroskop auf Fehler untersucht und auf ihre Spannungsfestigkeit hin getestet sowie gerahmt und in die Kammer eingesetzt. Mit der fertigen kleinen TPC mit GEM-basierter Auslese wurden IBF und Energieauflösung gemessen. Ziel der Messungen war es, einen möglichst geringen IBF von unter 1 % zu erhalten, um so wenig wie möglich Feldverzerrungen im Driftvolumen der TPC zu erhalten, bei gleichzeitig guter Energieauflösung von mindestens 12 %, um eine gute Teilchenidentifikation in der TPC sicherzustellen.
Da standard GEM-Konfigurationen mit nur drei GEM-Folien zwar eine gute Energieauflösung, jedoch zu viel IBF aufweisen, wurden die Messungen hauptsächlich mit vier GEM-Folien durchgeführt. Es wurden zwei verschiedene Arten von GEM-Folien verwendet, Standard (S) und Large-Pitch (LP) GEM-Folien, die bei einem Großteil der Messungen in der S-LP-LP-S-Konfiguration angeordnet waren.
Es wurde festgestellt, dass sich IBF und Energieauflösung gegenläufig verhalten, bei besser werdendem IBF also die Energieauflösung schlechter wird und umgekehrt.
Es wurden zwei verschiedene Gasmischungen, Ne-CO2-N2 (90-10-5) und Ar-CO2 (90-10), untersucht. Mit Neon wurde bei einem Gain von 2000 gemessen, mit Argon nur bei einem Gain von 1000, da bei Argon die Anzahl der produzierten Elektronen pro cm etwa doppelt so groß ist.
Der IBF war mit beiden Gasmischungen etwa gleich groß. Die Energieauflösung war mit Argon jedoch aufgrund des niedrigeren Gains erheblich schlechter. Mit Ne-CO2-N2 (90-10-5) gelang es, einen Arbeitspunkt mit einer Energieauflösung von etwa 12 % und einem IBF von unter 1 % zu finden, mit Ar-CO2 (90-10) war dies jedoch nicht der Fall.