arXiv subjects

J. Steinheimer

Publications and source records attributed to J. Steinheimer.

At least 19 recordsLinked to original sources

arXiv2026

Neutron Stars consistent Equations of State with Phase Transitions and their Impact in Heavy Ion Collision Observables

We explore the impact of different equations of state (EoS) on heavy ion collision observables using a Chiral Mean Field (CMF) framework constrained by astrophysical and lattice QCD inputs. The investigated family of EoS simultaneously reproduce neutron stars with masses above two solar masses and exhibit a first order phase transition around two times the nuclear saturation density. This is achieved by varying the relative vector and scalar couplings of $Δ$ resonances with the scalar $σ$ and vector $ω$ fields with respect to nucleons. These EoS are compared to the QCD trace anomaly at finite temperature. We implement both, the default CMF EoS and the modified EoS featuring a phase transition into the UrQMD transport model to study the effects of the phase transition on a qualitative and quantitative level. In particular Au+Au collisions at beam energies of 0.5-3 GeV, the GSI/FAIR energy range of the HADES and CBM experiments, shows visible sensitivity on the EoS. Transverse momentum distributions for protons, the directed flow ($v_1$) and its slope near mid-rapidity for $π^+$ as well as the $K^+/π^+$ ratio is analyzed. Clear differences emerge between the results obtained with the default CMF EoS, the modified EoS, and the cascade mode, particularly the slope of $v_1$ of the pions and in strangeness production. These findings demonstrate the sensitivity of heavy ion observables to the nuclear EoS and highlight potential experimental signatures of a phase transition.

nucl-th↗

arXiv2026

Hadron Physics Opportunities at FAIR

This White Paper outlines a coordinated, decade-spanning programme of hadron and QCD studies anchored at the GSI/FAIR accelerator complex. Profiting from intense deuteron, proton and pion beams coupled with high-rate capable detectors and an international theory effort, the initiative addresses fundamental questions related to the strong interaction featuring confinement and dynamical mass generation. This includes our understanding of hadron-hadron interactions and the composition of hadrons through mapping the baryon and meson spectra, including exotic states, and quantifying hadron structure. This interdisciplinary research connects topics in the fields of nuclear, heavy-ion, and (nuclear) astro (particle) physics, linking, for example, terrestrial data to constraints on neutron star structure. A phased roadmap with SIS100 accelerator start-up and envisaged detector upgrades will yield precision cross sections, transition form factors, in-medium spectral functions, and validated theory inputs. Synergies with external programmes at international accelerator facilities worldwide are anticipated. The programme is expected to deliver decisive advances in our understanding of non-perturbative (strong) QCD and astrophysics, and high-rate detector and data-science technology.

hep-ex↗

arXiv2023

Phase transition amplification of proton number fluctuations in nuclear collisions from a transport model approach

The time evolution of particle number fluctuations in nuclear collisions at intermediate energies ($E_{\rm lab} = 1.23-10A$ GeV) is studied by means of the UrQMD-3.5 transport model. The transport description incorporates baryonic interactions through a density-dependent potential. This allows for an implementation of a first order phase transition including a mechanically unstable region at large baryon density. The scaled variance of the baryon and proton number distributions is calculated in the central cubic spatial volume of the collisions at different times. A significant enhancement of fluctuations associated with the unstable region is observed. This enhancement persists to late times reflecting a memory effect for the fluctuations. The presence of the phase transition has a much smaller influence on the observable event-by-event fluctuations of protons in momentum space.

hep-ph↗

arXiv2022

Enhanced dilepton emission from a phase transition in dense matter

It is demonstrated that the presence of a phase transition in heavy ion collisions, at beam energies that probe dense QCD matter, leads to a significant enhancement of the dilepton yield per produced pion due to the extended emission time. In addition, the temperature of low mass dileptons shows a modest decrease due to the mixed phase. The emission of dileptons in the SIS18-SIS100 beam energies range is studied by augmenting the UrQMD transport model with a realistic density dependent equation of state, as well as two different phase transitions. This is achieved by extending the molecular dynamics interaction part of the UrQMD model to a density dependent interaction potential with a high density minimum leading to a phase transition and metastable coexisting high density states. Together with a high precision measurement these simulations will be able to constrain the existence of a phase transition in QCD up to densities of several times nuclear saturation density.

nucl-th↗

arXiv2022

Low Density Neutron Star Matter with Quantum Molecular Dynamics: The Role of Vector Interactions

The effect of isospin-dependent nuclear forces on the inner crust of neutron stars is modeled within the framework of Quantum Molecular Dynamics (QMD). To successfully control the density dependence of the symmetry energy of neutron-star matter below nuclear saturation density, a coupling potential between the $ω$ and $ρ$ meson fields is introduced. This approach is inspired by the baryon density and isospin density-dependent repulsive Skyrme force of asymmetric nuclear matter. In isospin-asymmetric nuclear matter, the system shows nucleation, as nucleons are arranged into shapes resembling nuclear pasta. The dependence of clusterization in the system on the isospin properties is also explored by calculating two-point correlation functions. We show that, as compared to previous results that did not involve the $ω$-$ρ$ potential, the energy symmetry slope $L$ is successfully controlled by varying the $ω$-$ρ$ coupling strength. Nevertheless, the effect of changing the slope of the nuclear symmetry energy $L$ on the crust-core transition density does not seem significant. To the knowledge of the authors, This is the first implementation of a $ω$-$ρ$ coupling in a QMD model for the inner crust of neutron stars.

nucl-th↗

arXiv2021

Hadronic resonance production and interaction in p-Pb collisions at LHC energies in EPOS3

Using the EPOS3 model with UrQMD to describe the hadronic phase, we study the production of short-lived hadronic resonances and the modification of their yields and $p_{T}$ spectra in p-Pb collisions at $\sqrt{s_{NN}}$ = 5.02 TeV. High-multiplicity p-Pb collisions exhibit similar behavior to mid-peripheral Pb-Pb collisions at LHC energies, and we find indications of a short-lived hadronic phase in p-Pb collisions that can modify resonance yields and $p_{T}$ spectra through scattering processes. The evolution of resonance production is investigated as a function of the system size, which is related to the lifetime of the hadronic phase, in order to study the onset of collective effects in p-Pb collisions. We also study hadron production separately in the core and corona parts of these collisions, and explore how this division affects the total particle yields as the system size increases.

nucl-th↗

arXiv2021

The possibility of twin star solutions in a model based on lattice QCD thermodynamics

The properties of compact stars and in particular the existence of twin star solutions are investigated within an effective model that is constrained by lattice QCD thermodynamics. The model is modified at large baryon densities to incorporate a large variety of scenarios of first order phase transitions to a phase of deconfined quarks. This is achieved by matching two different variants of the bag model equation of state, in order to estimate the role of the Bag model parameters on the appearance of a second family of neutron stars. The produced sequences of neutron stars are compared with modern constrains on stellar masses, radii, and tidal deformability from astrophysical observations and gravitational wave analyses. It is found that most of the possible scenarios disfavor a strong phase transition to quark matter and do not support the conjecture of a second family of neutron stars.

nucl-th↗

arXiv2018

Resonance production in high energy collisions from small to big systems

The aim of this paper is to understand resonance production (and more generally particle production) for different collision systems, namely proton-proton (pp), proton-nucleus (pA), and nucleus-nucleus (AA) scattering at the LHC. We will investigate in particular particle yields and ratios versus multiplicity, using the same multiplicity definition for the three different systems, in order to analyse in a compact way the evolution of particle production with the system size and the origin of a very different system size dependence of the different particles.

nucl-th↗

arXiv2018

Lattice-based QCD equation of state at finite baryon density: Cluster Expansion Model

The QCD equation of state at finite baryon density is studied in the framework of a Cluster Expansion Model (CEM), which is based on the fugacity expansion of the net baryon density. The CEM uses the two leading Fourier coefficients, obtained from lattice simulations at imaginary $μ_B$, as the only model input and permits a closed analytic form. Excellent description of the available lattice data at both $μ_B = 0$ and at imaginary $μ_B$ is obtained. We also demonstrate how the Fourier coefficients can be reconstructed from baryon number susceptibilities.

hep-lat↗

arXiv2017

Higher order net-proton number cumulants dependence on the centrality definition and other spurious effects

We study the dependence of the normalized moments of the net-proton multiplicity distributions on the definition of centrality in relativistic nuclear collisions at a beam energy of $\sqrt{s_{\mathrm{NN}}}= 7.7$ GeV. Using the UrQMD model as event generator we find that the centrality definition has a large effect on the extracted cumulant ratios. Furthermore we find that the finite efficiency for the determination of the centrality introduces an additional systematic uncertainty. Finally, we quantitatively investigate the effects of event-pile up and other possible spurious effects which may change the measured proton number. We find that pile-up alone is not sufficient to describe the data and show that a random double counting of events, adding significantly to the measured proton number, affects mainly the higher order cumulants in most central collisions.

nucl-th↗

arXiv2017

The application of the Quark-Hadron Chiral Parity-Doublet Model to neutron star matter

The Quark-Hadron Chiral Parity-Doublet model (Q$χ$P) is applied to calculate compact star properties in the presence of a deconfinement phase transition. Within this model, a consistent description of nuclear matter properties, chiral symmetry restoration, and a transition from hadronic to quark and gluonic degrees of freedom is possible within one unified approach. We find that the equation of state obtained is consistent with recent perturbative quantum chromodynamics (QCD) results and is able to accommodate observational constraints of massive and small neutron stars. Furthermore, we show that important features of the equation of state, such as the symmetry energy and its slope, are well within their observational constraints.

nucl-th↗

arXiv2017

Conserved charge fluctuations are not conserved during the hadronic phase

We study the correlation between the distributions of the net-charge, net-kaon, net-baryon and net-proton number at hadronization and after the final hadronic decoupling by simulating ultra relativistic heavy ion collisions with the hybrid version of the ultrarelativistic quantum molecular dynamics (UrQMD) model. We find that due to the hadronic rescattering these distributions are not strongly correlated. The calculated change of the correlation, during the hadronic expansion stage, does not support the recent paradigm, namely that the measured final moments of the experimentally observed distributions do give directly the values of those distributions at earlier times, when the system had been closer to the QCD crossover.

nucl-th↗

arXiv2017

Higher-order baryon number susceptibilities: interplay between the chiral and the nuclear liquid-gas transitions

We use an improved version of the SU(3) flavour parity-doublet quark-hadron model to investigate the higher order baryon number susceptibilities near the chiral and the nuclear liquid-gas transitions. The parity-doublet model has been improved by adding higher-order interaction terms of the scalar fields in the effective mean field Lagrangian, resulting in a much-improved description of nuclear ground-state properties, in particular the nuclear compressibility. The resulting phase diagram of the model agrees qualitatively with expectations from lattice QCD, i.e., it shows a crossover at zero net baryo-chemical potential and a critical point at finite density. Using this model, we investigate the dependence of the higher-order baryon number susceptibilities as function of temperature and chemical potential. We observe a strong interplay between the chiral and liquid-gas transition at intermediate baryo chemical potentials. Due to this interplay between the chiral and the nuclear liquid-gas transitions, the experimentally measured cumulants of the net baryon number may show very different beam energy dependence, subject to the actual freeze-out temperature.

nucl-th↗

arXiv2017

Formation of exotic baryon clusters in ultra-relativistic heavy-ion collisions

Recent experiments at RHIC and LHC have demonstrated that there are excellent opportunities to produce light baryonic clusters of exotic matter (strange and anti-matter) in ultra-relativistic ion collisions. Within the hybrid-transport model UrQMD we show that the coalescence mechanism can naturally explain the production of these clusters in the ALICE experiment at LHC. As a consequence of this mechanism we predict the rapidity domains where the yields of such clusters are much larger than the observed one at midrapidity. This new phenomenon can lead to unique methods for producing exotic nuclei.

nucl-th↗

arXiv2017

Influence of the hadronic phase on observables in ultrarelativistic heavy ion collisions

The hadronic phase in ultrarelativistic nuclear collisions has a large influence on final state observables like multiplicity, flow and $p_t$ spectra, as studied in the UrQMD approach. In this model one assumes that a non-equilibrium decoupling phase follows a fluid dynamical description of the high density phase. Hadrons are produced assuming local thermal equilibrium and dynamically decouple during the hadronic rescattering until the particles are registered in the detectors. This rescattering of hadrons modifies every hadronic bulk observable. The apparent multiplicity of resonances is suppressed as compared to a chemical equilibrium freeze-out model, because the decay products rescatter. Therefore the resonances, which decay in the early hadronic phase, cannot be identified anymore by the invariant mass method. Stable and unstable particles change their momentum distribution by more than 30$\%$ through rescattering and their multiplicity is modified by resonance production and annihilation on a similar magnitude. These findings show that it is all but trivial to conclude from the final state observables on the properties of the system at an earlier time where it may have been in local equilibrium.

nucl-th↗

arXiv2017

Sub-threshold charm production in nuclear collisions

We present the first predictions for sub-threshold open charm and charmonium production in nuclear collisions. The production mechanism is driven by multi-step scatterings of nucleons and their resonance states, accumulating sufficient energy for the production of $J/Ψ$, $Λ_c + \overline{D}$ and $D+\overline{D}$. Our results are of particular importance for the CBM experiment at FAIR, as they indicate that already at the SIS100 accelerator one can expect a significant number of charmed hadrons to be produced. This opens new possibilities to explore charm dynamics and the formation of charmed nuclei.

nucl-th↗

arXiv2016

Hadronization conditions in relativistic nuclear collisions and the QCD pseudo-critical line

We compare the reconstructed hadronization conditions in relativistic nuclear collisions in the nucleon-nucleon centre-of-mass energy range 4.7-2760 GeV in terms of temperature and baryon-chemical potential with lattice QCD calculations, by using hadronic multiplicities. We obtain hadronization temperatures and baryon chemical potentials with a fit to measured multiplicities by correcting for the effect of post-hadronization rescattering. The post-hadronization modification factors are calculated by means of a coupled hydrodynamical-transport model simulation under the same conditions of approximate isothermal and isochemical decoupling as assumed in the statistical hadronization model fits to the data. The fit quality is considerably better than without rescattering corrections, as already found in previous work. The curvature of the obtained "true" hadronization pseudo-critical line kappa is found to be 0.0048 +- 0.0026, in agreement with lattice QCD estimates; the pseudo-critical temperature at vanishing mu_B is found to be 164.3+-1.8 MeV.

nucl-th↗

arXiv2016

Formation of hypernuclei in heavy-ion collisions around the threshold energies

In relativistic ion collisions there are excellent opportunities to produce and investigate hyper-nuclei. We have systematically studied the formation of hypernuclear spectator residues in peripheral heavy-ion collisions with the transport DCM and UrQMD models. The hyperon capture was calculated within the potential and coalescence approaches. We demonstrate that even at the beam energies around and lower than the threshold for producing Lambda hyperons in binary nucleon-nucleon interactions a considerable amount of hypernuclei, including multi-strange ones, can be produced. This is important for preparation of new experiments on hypernuclei in the wide energy range. The uncertainties of the predictions are investigated within the models, and the comparison with the strangeness production measured in experiments is also performed.

nucl-th↗