arXiv subjects

M. Bleicher

Publications and source records attributed to M. Bleicher.

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 ${\Delta}$ resonances with the scalar ${\sigma}$ and vector ${\omega}$ 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 ${\pi}^+$ as well as the $K^+/{\pi}^+$ 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↗

arXiv2025

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↗

arXiv2024

Production of double strange hypernuclei and exotic nuclei in central Au+Au collisions at $\sqrt{s_{NN}}$=3 GeV

We extend the theoretical approach which includes the dynamical and statistical stages for the description of the nucleosynthesis in central collisions of relativistic ions. Previously, this approach was successfully applied to describe experimental data on both normal nuclei and single strange hypernuclei production in the GSI and RHIC-BES energy range. We predict the multiplicities of double strange hypernuclei up to $^4_{\Lambda \Lambda}$H and further intermediate mass nuclei up to $^8$Be for Au+Au central collisions at $\sqrt{s_{NN}}$=3 GeV, recently explored by the STAR experiments. These new nuclei can be identified by the measurement of the correlated particles coming after their decay. Such observations are a crucial test for the nucleosynthesis mechanism.

nucl-th↗

arXiv2024

Nucleation of baryons in relativistic hadron-nucleus collisions

We suggest a new theoretical method to describe the baryon clusterization of nuclei in hadron-nucleus reactions. As an example we have explored the nuclei production in $\pi^-+C$ and $\pi^-+W$ collisions at p$_{lab}$=1.7 GeV by using the hybrid approach consisting of the Ultra Relativistic Quantum Dynamics Model (UrQMD) and the Statistical Multifragmentation Model (SMM). The UrQMD describes the production of new baryons, and the propagation toward the subnuclear densities with the fluctuations leading to the formation of excited baryonic clusters. The SMM describes the production of final nuclei and hypernuclei after interaction of baryons inside these clusters. We demonstrate the transverse momenta, rapidity, mass distributions and excitation energies of both primary clusters and final nuclei (including hypernuclei). The results of the UrQMD and UrQMD+SMM model calculations for different clusterization parameters are compared with the available HADES experimental data on baryon production, providing a very promising window for future research on nuclei and hypernuclei formation in these reactions.

nucl-th↗

arXiv2023

Nucleosynthesis of light nuclei and hypernuclei in central Au+Au collisions at $\sqrt{s_{NN}}$=3 GeV

We analyze the experimental data on nuclei and hypernuclei yields recently obtained by the STAR collaboration. The hybrid dynamical and statistical approaches which have been developed previously are able to describe the experimental data reasonably. We discuss the intriguing difference between the yields of normal nuclei and hypernuclei which may be related to the properties of hypermatter at subnuclear densities. Most importantly new (hyper-)nuclei could be detected via particle correlations, and such measurements are relevant to pin down the production mechanism.

nucl-th↗

arXiv2023

Isospin compositions of correlated sources in the Fermi energy domain

Isotopic yield distributions of nuclei produced in peripheral collisions of $^{80}$Kr+$^{40,48}$Ca at 35 MeV/nucleon are studied. Experimental results obtained by the FAZIA Collaboration at the LNS facility in Catania are compared with calculations performed with the statistical multifragmentation model (SMM). The fragments with atomic number $Z=19-24$ observed at forward angles are successfully described with the ensemble method previously established for reactions at higher energy. Using the SMM results, the isotopic compositions of the projectile residues are reconstructed. The results indicate a significant isospin exchange between the projectile and target nuclei, not far from isospin equilibrium, during the initial phase of the reaction. The two groups of light fragments with $Z=1-4$, experimentally distinguished by their velocities relative to coincident heavy projectile fragments, are found to originate from different sources. The isotopic composition of the slower group is consistent with emission from a low-density neck, enriched in neutrons, and satisfactorily reproduced with SMM calculations for a corresponding neck source of small mass.

nucl-th↗

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

Evolution of the statistical disintegration of finite nuclei toward high energy

We develop a statistical approach for the description of complex nuclei formation from dynamically produced baryons in high energy heavy-ion reactions. We consider a finite highly-excited expanding nuclear system formed after central nucleus-nucleus collisions. This system is sub-divided into primary equilibrated nucleon clusters. The final nuclei are produced after the decay of these excited clusters. By the successful comparison with the FOPI experimental data we prove the possibility of such a local equilibrium in nuclear matter with the temperature corresponding to the phase coexistence region. The regularities obtained in this new nuclei production mechanism are shown.

nucl-th↗

arXiv2021

Triple nuclear collisions - a new method to explore the matter properties under new extreme conditions

We suggest to explore an entirely new method to experimentally and theoretically study the phase diagram of strongly interacting matter based on the triple nuclear collisions (TNC). We simulated the TNC using the UrQMD 3.4 model at the beam center-of-mass collision energies $\sqrt{s_{NN}} = 200$ GeV and $\sqrt{s_{NN}} = 2.76$ TeV. It is found that in the most central and simultaneous TNC the initial baryonic charge density is about 3 times higher than the one achieved in the usual binary nuclear collisions at the same energies. As a consequence, the production of protons and $Λ$-hyperons is increased by a factor of 2 and 1.5, respectively. Using the MIT Bag model equation we study the evolution of the central cell in TNC and demonstrate that for the top RHIC energy of collision the baryonic chemical potential is 2-2.5 times larger than the one achieved in the binary nuclear collision at the same type of reaction. Based on these estimates, we show that TNC offers an entirely new possibility to study the QCD phase diagram at very high baryonic charge densities.

hep-ph↗

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↗

arXiv2020

Coupling dynamical and statistical mechanisms for baryonic cluster production in nucleus collisions of intermediate and high energies

Central nucleus-nucleus collisions produce many new baryons and the nuclear clusters can be formed from these species. The phenomenological coalescence models were sufficiently good for description of light nuclei yields in a very broad range of collision energies. We demonstrate that in reality the coalescence process can be considered as 1) the formation of primary diluted excited baryon clusters and 2) their following statistical decay leading to the final cold fragment production. We argue that the formation of such excited systems from the interacting baryons is a natural consequence of the nuclear interaction at subnuclear densities resulting in the nuclear liquid-gas type phase transition in finite systems. In this way one can provide a consistent interpretation of the experimental fragment yields (FOPI data) including the important collision energy dependence in relativistic ion reactions. We investigate the regularities of this new kind of fragment production, for example, their yield, isospin, and kinetic energy characteristics. A generalization of such a clusterization mechanism for hypernuclear matter is suggested. The isotope yields and particle correlations should be adequate for studying these phenomena.

nucl-th↗

arXiv2020

On survey of nuclei and hypernuclei in multifragmentation

Multifragmentation reactions are dominating processes for the decomposition of highly excited nuclei leading to the fragment production in heavy-ion collisions. At high energy reactions strange particles are abundantly produced. We present a novel development of the Statistical multifragmentation model (SMM) as its generalization for the hyper-matter which is formed after the hyperon capture. In this way, it is possible to describe its disintegration into normal and hyper-nuclei. Some properties of hyper-nuclei and their binding energies can be determined from the comparison of the isotope yields. The main focus of this method is to investigate strange and multi-strange hypernuclei since their properties are not easy to measure in traditional hyper-nuclei experiments.

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↗

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

Production of light hypernuclei with light-ion beams and targets

Ion-ion collisions at relativistic energies have been shown recently to be a promising technique for the production of hypernuclei. In this article, we further investigate the production of light $Λ$ hypernuclei by use of a hybrid dynamical model, cascade-coalescence followed by Fermi breakup. The predictions are then compared with the available experimental data. The dependence of the production cross section upon the beam energy, beam mass number as well as different projectile-target combinations is investigated. In particular, we evaluate the yields and signal-over-background ratio in the invariant-mass spectrum for carbon projectiles impinging on hydrogen and carbon targets and various coincidence conditions in the experiment using the theoretical calculation as an input. It is found that comparing with carbon target, hydrogen target also leads to sizable hypernuclear yields, even for exotic species, and the hydrogen target could improve significantly signal-over-background ratio in some hypernuclear invariant mass studies.

nucl-th↗

arXiv2017

Evaluation of the hyperon binding energy via statistical production of hypernuclei

In nuclear reactions of high energy one can simultaneously produce a lot of hypernuclei after the capture of hyperons by nuclear residues. We consider statistical disintegration of such hypernuclear systems and the connection of fragment production with the binding energies of hyperons. It is demonstrated that the hyperon binding energies can be effectively evaluated from the yields of different isotopes of hypernuclei. The double ratio method is suggested for this purpose. The advantage of this procedure is its universality and the possibility to involve many different isotopes. This method can also be applied for multi-strange nuclei, which binding energies were very difficult to measure in previous hypernuclear experiments.

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

Three-fluid Hydrodynamics-based Event Simulator Extended by UrQMD final State interactions (THESEUS) for FAIR-NICA-SPS-BES/RHIC energies

We present a new event generator based on the three-fluid hydrodynamics (3FH) approach, followed by a particlization at the hydrodynamic decoupling surface and a subsequent UrQMD afterburner stage based on the microscopic UrQMD transport model that accounts for hadronic final state interactions. First results for Au+Au collisions are presented. The following topics are addressed: the directed flow, transverse-mass spectra, as well as rapidity distributions of protons, pions and kaons for two model equations of state, one with a first-order phase transition, the other with a crossover transition. Preliminary results on the femtoscopy are also discussed. We analyze the accuracy of reproduction of the 3FH results by the new event generator and the effect of the subsequent UrQMD afterburner stage.

nucl-th↗