arXiv subjects

S. Liebing

Publications and source records attributed to S. Liebing.

6 recordsLinked to original sources

arXiv2024

Cluster production and the chemical freeze-out in expanding hot dense matter

We discuss medium effects on light cluster production in the QCD phase diagram by relating Mott transition lines to those for chemical freeze-out. In heavy-ion collisions at highest energies provided by the LHC, light cluster abundances should follow the statistical model because of low baryon densities. Chemical freeze-out in this domain is correlated with the QCD crossover transition. At low energies, in the nuclear fragmentation region, where the freeze-out interferes with the liquid-gas phase transition, self-energy and Pauli blocking effects are important. We demonstrate that at intermediate energies the chemical freeze-out line correlates with the maximum mass fraction of nuclear bound states, in particular $\alpha$ particles. In this domain, the HADES, FAIR and NICA experiments can give new insights.

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arXiv2022

Quark-nuclear hybrid equation of state for neutron stars under modern observational constraints

We study a family of equations of state for hybrid neutron star matter. The hybrid EOS are obtained by a Maxwell construction of the first-order phase transition between a hadronic phase described by the relativistic density-functional EOS of the "DD2" class with excluded volume effects and a deconfined quark matter phase modeled by an instantaneous nonlocal version of the Nambu-Jona-Lasinio model in SU(2)$_f$ with vector interactions and color superconductivity. The form factor in the nonlocal quark matter model is fitted to lattice QCD results in the Coulomb gauge. Owing to strong coupling in the vector meson and diquark channels, a coexistence phase of color superconductivity and chiral symmetry breaking occurs. Our results show an approximately constant behavior for the squared speed of sound with values of 0.4 - 0.6 in the density region relevant for neutron star interiors. To simultaneously fulfill the constraints from the Neutron Star Interior Composition Explorer radius measurement for PSR J0740+6620 and tidal deformability from GW170817 it is necessary to consider a $\mu$-dependent bag pressure that mimics confinement.

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arXiv2021

Neutron stars with crossover to color superconducting quark matter

We follow the idea that the QCD phase diagram may be described by a crossover from a hadron resonance gas to perturbative QCD using the switch function ansatz of Albright, Kapusta and Young [1]. While the switch function could be calibrated at vanishing baryon chemical potential with data from lattice QCD simulations, it has been suggested recently by Kapusta and Welle [2] that in the zero temperature limit, the switch function parameter $\mu_0$ could be constrained by neutron star phenomenology, in particular by massive pulsars like PSR J0740+6620 with a mass exceeding $2~M_\odot$. In this work we demonstrate that this procedure to constrain the QCD phase diagram does crucially depend on the fact that cold dense quark matter is very likely in a color superconducting state.

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arXiv2020

QCD Phase Diagram at NICA energies: $K^+/\pi^+$ horn effect and light clusters in THESEUS

We discuss recent progress in the development of the three-fluid hydrodynamics-based program THESEUS towards an event generator suitable for applications to heavy-ion collisions at the intermediate energies of the planned NICA and FAIR experiments. We follow the strategy that modifications of particle distributions at the freeze-out surface in the QCD phase diagram may be mapped directly to the observable ones within a sudden freeze-out scheme. We report first results of these investigations for the production of light clusters (deuterons and tritons) which can be compared to experimental data from the HADES and the NA49 experiment and for the interpretation of the "horn" effect observed in the collision energy dependence of the $K^+/\pi^+$ ratio. Medium effects on light cluster production in the QCD phase diagram are negligible at the highest NICA energies but shall play a dominant role at the lowest energies. A sharp "horn"-type signal in the $K^+/\pi^+$ ratio can be obtained when the onset of Bose condensation modelled by a pion chemical potential results in an enhancement of pions at low momenta (which is seen at LHC energies) and would occur already in the NICA energy range.

hep-ph↗

arXiv2020

Strangeness and light fragment production at high baryon density

We discuss medium effects on light cluster production in the QCD phase diagram within a generalized Beth-Uhlenbeck (GBU) approach by relating Mott transition lines to those for chemical freeze-out. We find that in heavy-ion collisions at highest energies provided by the LHC light cluster abundances should follow the statistical model because of low baryon densities. At low energies in the nuclear fragmentation region, where the freeze-out interferes with the liquid-gas phase transition, selfenergy and Pauli blocking effects are important. At intermediate energies the HADES, FAIR and NICA experiments can give new information. The GBU approach provides new insights to strange hadron production in this energy domain for explaining the "horn" effects.

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arXiv2014

Composite Fermions in Medium: Extending the Lipkin Model

The role of phase space occupation effects for the formation of two- and three-particle bound states in a dense medium is investigated within an algebraic approach suitable for systems with short-range interactions. It is shown that for two-fermion bound states due to the account of the exchange symmetry (phase space occupation) effect (Pauli blocking) in a dense medium the binding energy is reduced and vanishes at a critical density (Mott effect). For three-fermion bound states, within a Faddeev equation approach, the intermediate formation of pair correlations leads to the representation as a suitably symmetrized fermion-boson bound state. It is shown that the Bose enhancement of fermion pairs can partially compensate the Pauli blocking between the fermions. This leads to the general result obtained by algebraic methods: three-fermion bound states in a medium with high phase space occupation appear necessarily as Borromean states beyond the Mott density of the two-fermion bound state.

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