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The production of K∗(892)± meson resonance is measured at midrapidity (|y|<0.5) in Pb−Pb collisions at √sNN=5.02 TeV using the ALICE detector at the CERN Large Hadron Collider. The resonance is reconstructed via its hadronic decay channel K∗(892)±→K0Sπ±. The transverse momentum distributions are obtained for various centrality intervals in the pT range of 0.4−16 GeV/c . Measurements of integrated yields, mean transverse momenta, and particle yield ratios are reported and found to be consistent with previous ALICE measurements for K∗(892)0 within uncertainties. The pT-integrated yield ratio 2K∗(892)±/(K++K−) in central Pb−Pb collisions shows a significant suppression at a level of 9.3σ relative to pp collisions. Thermal model calculations result in an overprediction of the particle yield ratio. Although both hadron resonance gas in partial chemical equilibrium (HRG-PCE) and music + smash simulations consider the hadronic phase, only HRG-PCE accurately represents the measurements, whereas music + smash simulations tend to overpredict the particle yield ratio. These observations, along with the kinetic freeze-out temperatures extracted from the yields measured for light-flavored hadrons using the HRG-PCE model, indicate a finite hadronic phase lifetime, which decreases with increasing collision centrality percentile. The pT-differential yield ratios 2K∗(892)±/(K++K−) and 2K∗(892)±/(π++π−) are presented and compared with measurements in pp collisions at √s=5.02 TeV. Both pa rticle ratios are found to be suppressed by up to a factor of five at pT<2.0 GeV/c in central Pb−Pb collisions and are qualitatively consistent with expectations for rescattering effects in the hadronic phase. The nuclear modification factor (RAA) shows a smooth evolution with centrality and is found to be below unity at pT>8 GeV/c, consistent with measurements for other light-flavored hadrons. The smallest values are observed in most central collisions, indicating larger energy loss of partons traversing the dense medium.
Long- and short-range correlations for pairs of charged particles are studied via two-particle angular correlations in pp collisions at s√=13 TeV and p−Pb collisions at sNN−−−√=5.02 TeV. The correlation functions are measured as a function of relative azimuthal angle Δφ and pseudorapidity separation Δη for pairs of primary charged particles within the pseudorapidity interval |η|<0.9 and the transverse-momentum interval 1<pT<4 GeV/c. Flow coefficients are extracted for the long-range correlations (1.6<|Δη|<1.8) in various high-multiplicity event classes using the low-multiplicity template fit method. The method is used to subtract the enhanced yield of away-side jet fragments in high-multiplicity events. These results show decreasing flow signals toward lower multiplicity events. Furthermore, the flow coefficients for events with hard probes, such as jets or leading particles, do not exhibit any significant changes compared to those obtained from high-multiplicity events without any specific event selection criteria. The results are compared with hydrodynamic-model calculations, and it is found that a better understanding of the initial conditions is necessary to describe the results, particularly for low-multiplicity events.
The inclusive production of the charm-strange baryon Ω0c is measured for the first time via its semileptonic decay into Ω−e+νe at midrapidity (|y| < 0.8) in proton–proton (pp) collisions at the centre-of-mass energy √s = 13 TeV with the ALICE detector at the LHC. The transverse momentum (pT) differential cross section multiplied by the branching ratio is presented in the interval 2 < pT < 12 GeV/c. The branching-fraction ratio BR(Ω0c → Ω−e+νe)/BR(Ω0c → Ω−π+) is measured to be 1.12 ± 0.22 (stat.) ± 0.27 (syst.). Comparisons with other experimental measurements, as well as with theoretical calculations, are presented.
The inclusive production of the charm-strange baryon Ω0c is measured for the first time via its semileptonic decay into Ω−e+νe at midrapidity (|y| < 0.8) in proton–proton (pp) collisions at the centre-of-mass energy √s = 13 TeV with the ALICE detector at the LHC. The transverse momentum (pT) differential cross section multiplied by the branching ratio is presented in the interval 2 < pT < 12 GeV/c. The branching-fraction ratio BR(Ω0c → Ω−e+νe)/BR(Ω0c → Ω−π+) is measured to be 1.12 ± 0.22 (stat.) ± 0.27 (syst.). Comparisons with other experimental measurements, as well as with theoretical calculations, are presented.
The knowledge of the material budget with a high precision is fundamental for measurements of direct photon production using the photon conversion method due to its direct impact on the total systematic uncertainty. Moreover, it influences many aspects of the charged-particle reconstruction performance. In this article, two procedures to determine data-driven corrections to the material-budget description in ALICE simulation software are developed. One is based on the precise knowledge of the gas composition in the Time Projection Chamber. The other is based on the robustness of the ratio between the produced number of photons and charged particles, to a large extent due to the approximate isospin symmetry in the number of produced neutral and charged pions. Both methods are applied to ALICE data allowing for a reduction of the overall material budget systematic uncertainty from 4.5% down to 2.5%. Using these methods, a locally correct material budget is also achieved. The two proposed methods are generic and can be applied to any experiment in a similar fashion.
The strong force is one of the four fundamental interactions, and the theory of it is called Quantum Chromodynamics (QCD). A many-body system of strongly interacting particles (QCD matter) can exist in different phases depending on temperature (T) and baryonic chemical potential (µB). The phases and transitions between them can be visualized as µB−T phase diagram. Extraction of the properties of the QCD matter, such as compressibility, viscosity and various susceptibilities, and its Equation of State (EoS) is an important aspect of the QCD matter study. In the region of near-zero baryonic chemical potential and low temperatures the QCD matter degrees of freedom are hadrons, in which quarks and gluons are confined, while at higher temperatures partonic (quarks and gluons) degrees of freedom dominate. This partonic (deconfined) state is called quark-gluon plasma (QGP) and is intensively studied at CERN and BNL. According to lattice QCD calculations at µB=0 the transition to QGP is smooth (cross-over) and takes place at T≈156 MeV. The region of the QCD phase diagram, where matter is compressed to densities of a few times normal nuclear density (µB of several hundreds MeV), is not accessible for the current lattice QCD calculations, and is a subject of intensive research. Some phenomenological models predict a first order phase transition between hadronic and partonic phases in the region of T≲100 MeV and µB≳500 MeV. Search for signs of a possible phase transition and a critical point or clarifying whether the smooth cross-over is continuing in this region are the main goals of the near future explorations of the QCD phase diagram.
In the laboratory a scan of the QCD phase diagram can be performed via heavy-ion collisions. The region of the QCD phase diagram at T≳150 MeV and µB≈0 is accessible in collisions at LHC energies (√sNN of several TeV), while the region of T≲100 MeV and µB≳500 MeV can be studied with collisions at √sNN of a few GeV. The QCD matter created in the overlap region of colliding nuclei (fireball) is rapidly expanding during the collision evolution. In the fireball there are strong temperature and pressure gradients, extreme electromagnetic fields and an exchange of angular momentum and spin between the system constituents. These effects result in various collective phenomena. Pressure gradients and the scattering of particles, together with the initial spatial anisotropy of the density distribution in the fireball, form an anisotropic flow - a momentum (azimuthal) anisotropy in the emission of produced particles. The correlation of particle spin with the angular momentum of colliding nuclei leads to a global polarization of particles. A strong initial magnetic field in the fireball results in a charge dependence and particle-antiparticle difference of flow and polarization.
Anisotropic flow is quantified by the coefficients vₙ from a Fourier decomposition of the azimuthal angle distribution of emitted particles relative to the reaction plane spanned by beam axis and impact parameter direction. The first harmonic coefficient v₁ quantifies the directed flow - preferential particle emission either along or opposite to the impact parameter direction. The v₁ is driven by pressure gradients in the fireball and thus probes the compressibility of the QCD matter. The change of the sign of v₁ at √sNN of several GeV is attributed to a softening of the EoS during the expansion, and thus can be an evidence of the first order phase transition. The global polarization coefficient PH is an average value of the hyperon’s spin projection on the direction of the angular momentum of the colliding system. It probes the dynamics of the QCD matter, such as vorticity, and can shed light on the mechanism of orbital momentum transfer into the spin of produced particles.
In collisions at √sNN of several GeV, which probe the region of the QCD phase diagram at T≲100 MeV and µB≳500 MeV, hadron production is dominated by u and d quarks. Hadrons with strange quarks are produced near the threshold, what makes their yields and dynamics sensitive to the density of the fireball. Thus measurement of flow and polarization, in particular of (multi-)strange particles, provides experimental constraints on the EoS, that allows to extract transport coefficients of the QCD matter from comparison of data with theoretical model calculations of heavy-ion collisions.
For continuation of the annotation see the PDF of thesis
The production of K∗(892)± meson resonance is measured at midrapidity (|y|<0.5) in Pb-Pb collisions at sNN−−−√=5.02 TeV using the ALICE detector at the LHC. The resonance is reconstructed via its hadronic decay channel K∗(892)±→K0Sπ±. The transverse momentum distributions are obtained for various centrality intervals in the pT range of 0.4-16 GeV/c. The reported measurements of integrated yields, mean transverse momenta, and particle yield ratios are consistent with previous ALICE measurements for K∗(892)0. The pT-integrated yield ratio 2K∗(892)±/(K++K−) in central Pb-Pb collisions shows a significant suppression (9.3σ) relative to pp collisions. Thermal model calculations overpredict the particle yield ratio. Although both simulations consider the hadronic phase, only HRG-PCE accurately represents the measurements, whereas MUSIC+SMASH tends to overpredict them. These observations, along with the kinetic freeze-out temperatures extracted from the yields of light-flavored hadrons using the HRG-PCE model, indicate a finite hadronic phase lifetime, which increases towards central collisions. The pT-differential yield ratios 2K∗(892)±/(K++K−) and 2K∗(892)±/(π++π−) are suppressed by up to a factor of five at pT<2 GeV/c in central Pb-Pb collisions compared to pp collisions at s√= 5.02 TeV. Both particle ratios and are qualitatively consistent with expectations for rescattering effects in the hadronic phase. The nuclear modification factor shows a smooth evolution with centrality and is below unity at pT>8 GeV/c, consistent with measurements for other light-flavored hadrons. The smallest values are observed in most central collisions, indicating larger energy loss of partons traversing the dense medium.
Off-central heavy-ion collisions are known to feature magnetic fields with magnitudes and characteristic gradients corresponding to the scale of the strong interactions. In this work, we employ equilibrium lattice simulations of the underlying theory, QCD, involving similar inhomogeneous magnetic field profiles to achieve a better understanding of this system. We simulate three flavors of dynamical staggered quarks with physical masses at a range of magnetic fields and temperatures, and extrapolate the results to the continuum limit. Analyzing the impact of the field on the quark condensate and the Polyakov loop, we find non-trivial spatial features that render the QCD medium qualitatively different as in the homogeneous setup, especially at temperatures around the transition. In addition, we construct leading-order chiral perturbation theory for the inhomogeneous background and compare its prediction to our lattice results at low temperature. Our findings will be useful to benchmark effective theories and low-energy models of QCD for a better description of peripheral heavy-ion collisions.
ATP-binding cassette (ABC) transporters shuttle diverse substrates across biological membranes. They play a role in many physiological processes but are also the reason for antibiotic resistance of microbes and multi drug resistance in cancer, and their dysfunction can lead to serious diseases. Transport is achieved through an ATP-driven closure of the two nucleotide binding sites (NBSs) which induces a transition between an inward-facing (IF) and an outward-facing (OF) conformation of the connected transmembrane domains (TMDs). In contrast to this forward transition, the reverse transition (OF-to-IF) that involves Mg2+-dependent ATP hydrolysis and release is less understood. This is particularly relevant for heterodimeric ABC transporters with asymmetric NBSs. These transporters possess an ATPase active consensus NBS (c-NBS) and a degenerate NBS (d-NBS) with little or no ATPase activity.
Crucial details regarding function and mechanism of the transport cycle remain elusive.
Here, these open questions were addressed using pulse electron-electron double resonance (PELDOR or DEER) spectroscopy of the heterodimeric ABC exporter TmrAB.
To better understand the transport cycle, the underlying kinetics of the conformational transitions need to be elucidated. By introducing paramagnetic nitroxide (NO) spin probes at key positions of TmrAB and employing time-resolved PELDOR spectroscopy, the forward transition could be followed over time and the rate constants for the conformational transition at the TMDs and NBSs were characterized.
The temperature dependence of these rate constants was further analyzed to determine for the first time the activation energy of conformational changes in a large membrane protein. For TMD opening and c-NBS dimerization, values of 75 ± 27 kJ/mol and 56 ± 3 kJ/mol, respectively were found. These values agree with reported activation energies of peptide transport and peptide dissociation in other ABC transporters, suggesting that the forward transition may be the rate-limiting step for substrate translocation.
The functional relevance of asymmetric NBSs is so far not well understood. By combining Mg2+-to-Mn2+ substitution with Mn2+-NO and NO-NO PELDOR spectroscopy, the binding of ATP-Mn2+, the conformation of the NBSs, and the conformation of the TMDs could be simultaneously monitored for the first time. These results reveal an asymmetric post-hydrolytic state. Time-resolved investigation showed that ATP hydrolysis at the active c-NBS triggers the reverse transition, whereas opening of the impaired d-NBS regulates the return to the IF conformation.
The total charm-quark production cross section per unit of rapidity dσ(cc)/dy, and the fragmentation fractions of charm quarks to different charm-hadron species f(c → hc), are measured for the first time in p–Pb collisions at √sNN = 5.02 TeV at midrapidity (−0.96 < y < 0.04 in the centre-ofmass frame) using data collected by ALICE at the CERN LHC. The results are obtained based on all the available measurements of prompt production of ground-state charm-hadron species: D0, D+,D+s, and J/ψ mesons, and Λ+cand Ξ0cbaryons. The resulting cross section is dσ(cc)/dy = 219.6±6.3 (stat.)+10.5−11.8(syst.)+7.6−2.9(extr.)±5.4 (BR)±4.6 (lumi.)±19.5 (rapidity shape) +15.0 (Ω0c) mb, which is consistent with a binary scaling of pQCD calculations from pp ollisions. The measured fragmentation fractions are compatible with those measured in pp collisions at √s = 5.02 and 13 TeV, showing an increase in the relative production rates of charm baryons with respect to charm mesons in pp and p–Pb collisions compared with e+e − and e−p collisions. The pT-integrated nuclear modification factor of charm quarks, RpPb(cc) = 0.91±0.04 (stat.) +0.08 −0.09 (syst.) +0.04 −0.03 (extr.)±0.03 (lumi.), is found to be consistent with unity and with theoretical predictions including nuclear modifications of the parton distribution functions.
This work aims to differentiate strangeness produced from hard processes (jet-like) and softer processes (underlying event) by measuring the angular correlation between a high-momentum trigger hadron (h) acting as a jet-proxy and a produced strange hadron (φ(1020) meson). Measuring h–φ correlations at midrapidity in p–Pb collisions at √sNN = 5.02 TeV as a function of event multiplicity provides insight into the microscopic origin of strangeness enhancement in small collision systems. The jet-like and the underlying-event-like strangeness production are investigated as a function of event multiplicity. They are also compared between a lower and higher momentum region. The evolution of the per-trigger yields within the near-side (aligned with the trigger hadron) and away-side (in the opposite direction of the trigger hadron) jet is studied separately, allowing for the characterization of two distinct jet-like production regimes. Furthermore, the h–φ correlations within the underlying event give access to a production regime dominated by soft production processes, which can be compared directly to the in-jet production. Comparisons between h–φ and dihadron correlations show that the observed strangeness enhancement is largely driven by the underlying event, where the φ/h ratio is significantly larger than within the jet regions. As multiplicity increases, the fraction of the total φ(1020) yield coming from jets decreases compared to the underlying event production, leading to high-multiplicity events being dominated by the increased strangeness production from the underlying event
We present a relativistic Shakhov-type generalization of the Anderson-Witting relaxation time model for the Boltzmann collision integral to modify the ratio of momentum diffusivity to thermal diffusivity. This is achieved by modifying the path on which the single particle distribution function fk approaches local equilibrium f0k by constructing an intermediate Shakhov-type distribution fSk similar to the 14-moment approximation of Israel and Stewart. We illustrate the effectiveness of this model in case of the Bjorken expansion of an ideal gas of massive particles and the damping of longitudinal waves through an ultrarelativistic ideal gas.
Das radioaktive Edelgas Radon und seine ebenfalls radioaktiven Zerfallsprodukte machen den größten Teil der natürlichen Strahlenbelastung in Deutschland aus. Trotz der Einstufung als krebserregend für Lungenkrebs wird es zur Therapie entzündlicher Krankheiten eingesetzt. Der hauptsächliche Aufnahmemechanismus ist dabei die Inkorporation über die Atmung, wobei Radon auch über die Haut aufgenommen werden kann. Radon wird dabei über das Blut im gesamten Körper verteilt und kann in Gewebe mit hoher Radonlöslichkeit akkumulieren. Die Zerfallsprodukte verbleiben jedoch in der Lunge, zerfallen dort, bevor sie abtransportiert werden können und schädigen das dortige Gewebe.
Die Lungendosis wird laut Simulationen zum größten Teil durch die kleinsten Radon-Zerfallsprodukte (< 10 nm) bestimmt, die besonders effektiv im Respirationstrakt anheften. Die erzeugte Dosis ist dabei aufgrund der inhomogenen Anlagerung der Zerfallsprodukte lokal stark variabel. In Simulationen wurden Bifurkationen als Ort besonders hoher Deposition identifiziert, wobei die experimentelle Datenlage zur Deposition kleinster Radon-Zerfallsprodukte eingeschränkt ist. Aufgrund des Anstiegs der Komplexität von Simulationen oder Experimenten wird in den meisten Betrachtungen nicht der oszillatorische Atemzyklus berücksichtigt, sondern lediglich ein einseitig gerichteter Luftstrom betrachtet. Im Rahmen dieser Arbeit wurde ein experimentelles Modell entwickelt und etabliert, das die Messung der Deposition von Radon-Zerfallsprodukten ermöglicht und zwischen drei Größenfraktionen (Freie Zerfallsprodukte: < 10 nm, Cluster: 20-100 nm, Angelagerte Zerfallsprodukte: > 100 nm) unterscheiden kann. Der Luftfluss durch das Modell bildet sowohl die Inhalation als auch die Exhalation ab. Erste Experimente mit dem neu entwickelten Messaufbau konnten die aus Simulationen bekannte erhöhte Deposition der freien Zerfallsprodukte in einer Bifurkation abbilden. Die Vergrößerung des Bifurkationswinkels von 70° auf 180° zeigte lediglich einen minimalen Anstieg in der Größenordnung des Messfehlers. Der dominierende Prozess der Anlagerung der freien Zerfallsprodukte ist die Brown'sche Molekularbewegung, die unabhängig vom Bifurkationswinkel ist. Dennoch kann ein veränderter Winkel die Luftströmung und entstehende Turbulenzen verändern, wodurch die Deposition beeinflusst werden kann. Dies lässt sich jedoch mit dem hier benutzten Messaufbau nicht auflösen. Entgegen der Beobachtungen in der Literatur führte die Erhöhung der Atemfrequenz von 12 auf 30 Atemzüge pro Minute, in den im Rahmen dieser Arbeit durchgeführten Experimenten, zu keiner messbaren Veränderung der Deposition. Diese Beobachtung ist auf die Entstehung gegensätzlicher Effekte zurückzuführen. Einerseits führt eine schnellere Luftströmung zu kürzeren Aufenthaltszeiten der freien Zerfallsprodukte im Modell, wodurch die Deposition unwahrscheinlicher wird. Andererseits entstehen vermehrt sekundäre Strömungen und absolut betrachtet werden mehr Partikel durch das Modell gepumpt. Es ist davon auszugehen, dass sich diese Effekte im hier getesteten Bereich aufheben.
Als potentielle Schutzmaßnahme zur Reduktion der Lungendosis konnte im Rahmen dieser Arbeit die Filtereffzienz von Gesichtsmasken (OP-Masken, FFP2 Masken) gegenüber Radon und seinen Zerfallsprodukten bestimmt werden. Während Radon nicht gefiltert wird, wurden die freien Zerfallsprodukte fast vollständig (> 98%) und die Cluster zum größten Teil (≈ 80 %) zurückgehalten.
Radon selbst kann im gesamten Organismus verteilt werden und dort in Gewebe akkumulieren. Zur Bestimmung der Dosis wird dabei auf biokinetische Modelle zurückgegriffen. Diese sind von der Qualität ihrer Eingabeparameter abhängig, wobei beispielsweise die Werte zur Verteilung von Radon zwischen Blut und Gewebe auf experimentell gewonnenen Löslichkeitswerten aus Mäusen und Ratten beruhen. Unbekannte Werte werden von der Internationalen Strahlenschutzkommission basierend auf der Gewebezusammensetzung als gewichteter Mittelwert berechnet. In dieser Arbeit wurde die Löslichkeit in humanen Blutproben und wässrigen Lösungen verschiedener Konzentrationen der Blutproteine Hämoglobin und Albumin bestimmt. Es löste sich mehr Radon in Plasma als in Erythrozytenkonzentrat und Vollblut. Die Protein-Lösungen zeigten keine Konzentrationsabhängigkeit der Löslichkeit, sondern lediglich in hitzedenaturiertem Hämoglobin wurde eine niedrigere Löslichkeit gemessen. Basierend auf diesen Beobachtungen, sollte die These überprüft werden, ob sich die Löslichkeit einer Mischung als gewichteter Mittelwert der einzelnen Löslichkeiten berechnen lässt. Daher wurden diese in einer Mischung aus zwei Flüssigkeiten (1-Pentanol, Ölsäure) bestimmt. Die experimentell bestimmte Löslichkeit war dabei fast doppelt so groß wie der berechnete Wert. Dieser Unterschied kann dadurch zustande kommen, dass bei einer Berechnung basierend auf der Zusammensetzung die Wechselwirkungen zwischen den Lösungsmitteln vernachlässigt werden. Dies verdeutlicht die Notwendigkeit experimenteller Daten zur Verteilung und Lösung von Radon in verschiedenem Gewebe.
We measure the Born cross section for the reaction e+e−→ηhc from s√=4.129 to 4.600~GeV using data sets collected by the BESIII detector running at the BEPCII collider. A resonant structure in the cross section line shape near 4.200~GeV is observed with a statistical significance of 7σ. The parameters of this resonance are measured to be \MeasMass\ and \MeasWidth, where the first uncertainties are statistical and the second systematic.
Motivated by the on-going discussion on the nature of magnetism in the quantum Ising chain CoNb2O6, we present a first-principles-based analysis of its exchange interactions by applying an \textit{ab initio} approach with additional modelling that accounts for various drawbacks of a purely density functional theory ansatz. With this method we are able to extract and understand the origin of the magnetic couplings under inclusion of all symmetry-allowed terms, and to resolve the conflicting model descriptions in CoNb2O6. We find that the twisted Kitaev chain and the transverse-field ferromagnetic Ising chain views are mutually compatible, although additional off-diagonal exchanges are necessary to provide a complete picture. We show that the dominant exchange interaction is a ligand-centered exchange process - involving the eg electrons -, which is rendered anisotropic by the low-symmetry crystal fields environments in CoNb2O6, giving rise to the dominant Ising exchange, while the smaller bond-dependent anisotropies are found to originate from d−d kinetic exchange processes involving the t2g electrons. We demonstrate the validity of our approach by comparing the predictions of the obtained low-energy model to measured THz and inelastic neutron scattering spectra.
he family of cubic noncentrosymmetric 3-4-3 compounds has become a fertile ground for the discovery of novel correlated metallic and insulating phases. Here, we report the synthesis of a new heavy fermion compound, Ce3Bi4Ni3. It is an isoelectronic analog of the prototypical Kondo insulator Ce3Bi4Pt3 and of the recently discovered Weyl-Kondo semimetal Ce3Bi4Pd3. In contrast to the volume-preserving Pt-Pd substitution, structural and chemical analyses reveal a positive chemical pressure effect in Ce3Bi4Ni3 relative to its heavier counterparts. Based on the results of electrical resistivity, Hall effect, magnetic susceptibility, and specific heat measurements, we identify an energy gap of 65–70 meV, about eight times larger than that in Ce3Bi4Pt3 and about 45 times larger than that of the Kondo-insulating background hosting the Weyl nodes in Ce3Bi4Pd3. We show that this gap as well as other physical properties do not evolve monotonically with increasing atomic number, i.e., in the sequence Ce3Bi4Ni3−Ce3Bi4Pd3−Ce3Bi4Pt3, but instead with increasing partial electronic density of states of the 𝑑 orbitals at the Fermi energy. This work opens the possibility to investigate the conditions under which topological states develop in this series of strongly correlated 3-4-3 materials.
The family of cubic noncentrosymmetric 3-4-3 compounds has become a fertile ground for the discovery of novel correlated metallic and insulating phases. Here, we report the synthesis of a new heavy fermion compound, Ce3Bi4Ni3. It is an isoelectronic analog of the prototypical Kondo insulator Ce3Bi4Pt3 and of the recently discovered Weyl-Kondo semimetal Ce3Bi4Pd3. In contrast to the volume-preserving Pt-Pd substitution, structural and chemical analyses reveal a positive chemical pressure effect in Ce3Bi4Ni3 relative to its heavier counterparts. Based on the results of electrical resistivity, Hall effect, magnetic susceptibility, and specific heat measurements, we identify an energy gap of 65-70 meV, about eight times larger than that in Ce3Bi4Pt3 and about 45 times larger than that of the Kondo-insulating background hosting the Weyl nodes in Ce3Bi4Pd3. We show that this gap as well as other physical properties do not evolve monotonically with increasing atomic number, i.e., in the sequence Ce3Bi4Ni3-Ce3Bi4Pd3-Ce3Bi4Pt3, but instead with increasing partial electronic density of states of the d orbitals at the Fermi energy. To understand under which condition topological states form in these materials is a topic for future studies.
Heterostructures of graphene in proximity to magnetic insulators open the possibility to investigate exotic states emerging from the interplay of magnetism, strain and charge transfer between the layers. Recent reports on the growth of self-integrated atomic wires of β-RuCl3 on graphite suggest these materials as versatile candidates to investigate these effects. Here we present detailed first principles calculations on the charge transfer and electronic structure of β-RuCl3/heterostructures and provide a comparison with the work function analysis of the related honeycomb family members α-RuX3 (X = Cl,Br,I). We find that proximity of the two layers leads to a hole-doped graphene and electron-doped RuX3 in all cases, which is sensitively dependent on the distance between the two layers. Furthermore, strain effects due to lattice mismatch control the magnetization which itself has a strong effect on the charge transfer. Charge accumulation in β-RuCl3 strongly drops away from the chain making such heterostructures suitable candidates for sharp interfacial junctions in graphene-based devices.
canning tunneling microscopy (STM) is perhaps the most promising way to detect the superconducting gap size and structure in the canonical unconventional superconductor Sr2RuO4 directly. However, in many cases, researchers have reported being unable to detect the gap at all in simple STM conductance measurements. Recently, an investigation of this issue on various local topographic structures on a Sr-terminated surface found that superconducting spectra appeared only in the region of small nanoscale canyons, corresponding to the removal of one RuO surface layer. Here, we analyze the electronic structure of various possible surface structures using first principles methods, and argue that bulk conditions favorable for superconductivity can be achieved when removal of the RuO layer suppresses the RuO4 octahedral rotation locally. We further propose alternative terminations to the most frequently reported Sr termination where superconductivity surfaces should be observed.
Motivated by recently reported magnetic-field induced topological phases in ultracold atoms and correlated Moiré materials, we investigate topological phase transitions in a minimal model consisting of interacting spinless fermions described by the Hofstadter model on a square lattice. For interacting lattice Hamiltonians in the presence of a commensurate magnetic flux it has been demonstrated that the quantized Hall conductivity is constrained by a Lieb-Schultz-Mattis (LSM)-type theorem due to magnetic translation symmetry. In this work, we revisit the validity of the theorem for such models and establish that a topological phase transition from a topological to a trivial insulating phase can be realized but must be accompanied by spontaneous magnetic translation symmetry breaking caused by charge ordering of the spinless fermions. To support our findings, the topological phase diagram for varying interaction strength is mapped out numerically with exact diagonalization for different flux quantum ratios and band fillings using symmetry indicators. We discuss our results in the context of the LSM-type theorem.
The absolute branching fraction of the decay Λc(2625)+→Λ+cπ+π− is measured for the first time to be (50.7±5.0stat.±4.9syst.)% with 368.48 pb−1 of e+e− collision data collected by the BESIII detector at the center-of-mass energies of s√=4.918 and 4.950 GeV. This result is lower than the naive prediction of 67\%, obtained from isospin symmetry, by more than 2σ, thereby indicating that the novel mechanism referred to as the \textit{threshold effect}, proposed for the strong decays of Λc(2595)+, also applies to Λc(2625)+. This measurement is necessary to obtain the coupling constants for the transitions between s-wave and p-wave charmed baryons in heavy hadron chiral perturbation theory. In addition, we search for the decay Λc(2595)+→Λ+cπ+π−. No significant signal is observed, and the upper limit on its branching fraction is determined to be 80.8\% at the 90\% confidence level.
The production cross section of inclusive isolated photons has been measured by the ALICE experiment at the CERN LHC in pp collisions at centre-of-momentum energy of s√=13 TeV collected during the LHC Run 2 data-taking period. The measurement is performed by combining the measurements of the electromagnetic calorimeter EMCal and the central tracking detectors ITS and TPC, covering a pseudorapidity range of |ηγ|<0.67 and a transverse momentum range of 7<pγT<200 GeV/c. The result extends to lower pγT and xγT=2pγT/s√ ranges, the lowest xγT of any isolated photon measurements to date, extending significantly those measured by the ATLAS and CMS experiments towards lower pγT at the same collision energy with a small overlap between the measurements. The measurement is compared with next-to-leading order perturbative QCD calculations and the results from the ATLAS and CMS experiments as well as with measurements at other collision energies. The measurement and theory prediction are in agreement with each other within the experimental and theoretical uncertainties.
The PhD addresses the feasibility of reconstructing open charm mesons with the Compressed Baryonic Matter experiment, which will be installed at the FAIR accelerator complex at Darmstadt/Germany. The measurements will be carried out by means of a dedicated Micro Vertex Detector (MVD), which will be equipped with CMOS Monolithic Active Pixel Sensors (MAPS). The feasibility of reconstructing the particles with a proposed detector setup was studied.
To obtain conclusive results, the properties of a MAPS prototype were measured in a beam test at the CERN-SPS accelerator. Based on the results achieved, a dedicated simulation software for the sensors was developed and implemented into the software framework of CBM (CBMRoot). Simulations on the reconstruction of D0-mesons were carried out. It is concluded that the reconstruction of those particles is possible.
The PhD introduces the physics motivation of doing open charm measurements, represents the results of the measurements of MAPS and introduces the innovative simulation model for those sensors as much as the concept and results of simulations of the D0 reconstruction.
Most elements heavier than iron are synthesized in stars during neutron capture reactions in the r- and s-process. The s-process nucleosynthesis is composed of the main and weak component. While the s-process is considered to be well understood, further investigations using nucleosynthesis simulations rely on measured neutron capture cross sections as crucial input parameters. Neutron capture cross sections
relevant for the s-process can be measured using various experimental methods. A prominent example is the activation method relying on the 7Li(p,n)7Be reaction as a neutron source, which has the advantage of high neutron intensities and is able to create a quasi-stellar neutron spectrum at kBT = 25 keV. Other neutron sources able to provide quasi-stellar spectra at different energies suffer from lower neutron intensities. Simulations using the PINO tool suggest the neutron activation of samples with different neutron spectra, provided by the 7Li(p,n)7Be reaction, and a subsequent linear combination of the obtained spectrum-averaged cross sections
to determine the Maxwellian-averaged cross section (MACS) at various energies of astrophysical relevance. To investigate the accuracy of the PINO tool at proton energies between the neutron emission threshold at Ep = 1880.4 keV and 2800 keV,
measurements of the 7Li(p,n)7Be neutron fields are presented, which were carried out at the PTB Ion Accelerator Facility at the Physikalisch-Technische Bundesanstalt in Braunschweig. The neutron fields of ten different proton energies were measured.
The presented neutron fields show a good agreement at proton energies Ep = 1887, 1897, 1907, 1912 and 2100 keV. For the other proton energies, E p = 2000, 2200, 2300, 2500, and 2800 keV, differences between measurement and simulation were found and discussed. The obtained results can be used to benchmark and adapt the PINO tool and provide crucial information for further improvement of the neutron activation method for astrophysics.
An application for the 7Li(p,n)7Be neutron fields is presented as an activation experiment campaign of gallium, an element that is mostly produced during the weak s-process in massive stars. The available cross section data for the 69,71Ga(n,γ)
reactions, mostly determined by activation measurements, show differences up toa factor of three. To improve the data situation, activation measurements were carried out using the 7Li(p,n)7Be reaction. The neutron capture cross sections for
a quasi-stellar neutron spectrum at kBT = 25 keV were determined for 69Ga and 71Ga.