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J. Aichelin

Publications and source records attributed to J. Aichelin.

At least 19 recordsLinked to original sources
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

Cluster formation near midrapidity -- can the mechanism be identified experimentally?

The formation of weakly bound clusters in the hot and dense environment at midrapidity is one of the surprising phenomena observed experimentally in heavy-ion collisions from a low center of mass energy of a few GeV up to a ultra-relativistic energy of several TeV. Three approaches have been advanced to describe the cluster formation: coalescence at kinetic freeze-out, cluster formation during the entire heavy-ion collision by potential interaction between nucleons and deuteron production by hadronic reactions. We identify experimental observables, which can discriminate these production mechanisms for deuterons.

nucl-th↗
arXiv2020

Parton-Hadron-Quantum-Molecular Dynamics (PHQMD) -- A Novel Microscopic N-Body Transport Approach for Heavy-Ion Collisions, Dynamical Cluster Formation and Hypernuclei Production

Cluster and hypernuclei production in heavy-ion collisions is presently under active experimental and theoretical investigation. Since clusters are weekly bound objects, their production is very sensitive to the dynamical evolution of the system and its interactions. The theoretical description of cluster formation is related to the n-body problem. Here we present the novel n-body dynamical transport approach PHQMD (Parton-Hadron-Quantum-Molecular Dynamics) which is designed to provide a microscopic description of nuclear cluster and hypernucleus formation as well as of general particle production in heavy-ion reactions at relativistic energies. In difference to the coalescence or statistical models, often used for the cluster formation, in PHQMD clusters are formed dynamically due to the interactions between baryons described on a basis of Quantum Molecular Dynamics (QMD)which allows to propagate the n-body Wigner density and n-body correlations in phase-space, essential for the cluster formation. The clusters are identified by the MST (Minimum Spanning Tree) or the SACA ('Simulated Annealing Cluster Algorithm') algorithm which finds the most bound configuration of nucleons and clusters. Collisions among hadrons as well as Quark-Gluon-Plasma formation and parton dynamics in PHQMD are treated in the same way as in the established PHSD (Parton-Hadron-String Dynamics)transport approach. In order to verify our approach with respect to the general dynamics we present here the first PHQMD results for general 'bulk' observables such as rapidity distributions and transverse mass spectra for hadrons ($π, K, \bar K, p, \bar p, Λ, \bar Λ$) from SIS to RHIC energies. We find a good description of the 'bulk' dynamics which allows us to proceed with the results on cluster production, including hypernuclei.

nucl-th↗
arXiv2019

Parton Hadron Quantum Molecular Dynamics (PHQMD) -- a Novel Microscopic N-Body Transport Approach for Heavy-Ion Dynamics and Hypernuclei Production

We present the novel microscopic n-body dynamical transport approach PHQMD(Parton-Hadron-Quantum-Molecular-Dynamics) for the description of particle production and cluster formation in heavy-ion reactions at relativistic energies. The PHQMD extends the established PHSD (Parton-Hadron-String-Dynamics) transport approach by replacing the mean field by density dependent two body interactions in a similar way as in the Quantum Molecular Dynamics (QMD) models. This allows for the calculation of the time evolution of the n-body Wigner density and therefore for a dynamical description of clusters and hypernuclei formation. The clusters are identified with the MST ('Minimum Spanning Tree') or the SACA ('Simulated Annealing Cluster Algorithm') algorithm which - by regrouping the nucleons in single nucleons and noninteracting clusters - finds the most bound configuration of nucleons and clusters. The selected results on clusters and hypernuclei production from Ref. arXiv:1907.03860 are discussed in this contribution.

nucl-th↗
arXiv2019

The PHQMD model for the formation of nuclear clusters and hypernuclei in heavy-ion collisions

Modeling of the process of the formation of nuclear clusters in the hot nuclear matter is a challenging task. We present the novel n-body dynamical transport approach - PHQMD (Parton-Hadron-Quantum-Molecular Dynamics) [1] for the description of heavy-ion collisions as well as clusters and hpernuclei formation. The PHQMD extends well established PHSD (Parton-Hadron-String Dynamics) approach - which incorporates explicit partonic degrees-of-freedom (quarks and gluons), an equation-of-state from lattice QCD, as well as dynamical hadronization and hadronic elastic and inelastic collisions in the final reaction phase, by n-body quantum molecular dynamic propagation of hadrons which allows choosing of the equation of state with different compression modulus. The formation of clusters, including hypernuclei, is realized by incorporation the Simulated Annealing Clusterization Algorithm (SACA). We present first results from PHQMD on the study of the production rates of strange hadrons, nuclear clusters and hypernuclei in e1elementary and heavy-ion collisions at NICA energies. In particular, sensitivity on the "hard" and "soft" equation of state within the PHQMD model was investigated for "bulk" observables.

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arXiv2019

FRIGA, A New Approach To Identify Isotopes and Hyper-nuclei In N-Body Transport Models

We present a new approach to identify fragments in computer simulations of relativistic heavy ion collisions. It is based on the simulated annealing technique and can be applied to n-body transport models like the Quantum Molecular Dynamics. This new approach is able to predict isotope yields as well as hyper-nucleus production. In order to illustrate its predicting power, we confront this new method with experimental data and show the sensitivity on the parameters which govern the cluster formation.

nucl-th↗
arXiv2019

Future physics opportunities for high-density QCD at the LHC with heavy-ion and proton beams

The future opportunities for high-density QCD studies with ion and proton beams at the LHC are presented. Four major scientific goals are identified: the characterisation of the macroscopic long wavelength Quark-Gluon Plasma (QGP) properties with unprecedented precision, the investigation of the microscopic parton dynamics underlying QGP properties, the development of a unified picture of particle production and QCD dynamics from small (pp) to large (nucleus--nucleus) systems, the exploration of parton densities in nuclei in a broad ($x$, $Q^2$) kinematic range and the search for the possible onset of parton saturation. In order to address these scientific goals, high-luminosity Pb-Pb and p-Pb programmes are considered as priorities for Runs 3 and 4, complemented by high-multiplicity studies in pp collisions and a short run with oxygen ions. High-luminosity runs with intermediate-mass nuclei, for example Ar or Kr, are considered as an appealing case for extending the heavy-ion programme at the LHC beyond Run 4. The potential of the High-Energy LHC to probe QCD matter with newly-available observables, at twice larger center-of-mass energies than the LHC, is investigated.

hep-ph↗
arXiv2018

The influence of the neutron skin and the asymmetry energy on the $π^-/π^+$ ratio

We use the Isospin Quantum Molecular Dynamics model (IQMD) to analyze the centrality dependence of the isospin ratio of pions, $π^-/π^+$. We find that the density dependence of the asymmetry potential, the Pauli blocking of the $Δ$-decay and the thickness of the neutron skin influence in different ways this observable. Using the centrality dependence of this ratio at different beam energies we can disentangle the different contributions and open the way for their experimental determination.

nucl-th↗
arXiv2018

On the Origin of the Elliptic Flow and its Dependence on the Equation of State in Heavy Ion Reactions at Intermediate Energies

Recently it has been discovered that the elliptic flow, v2, of composite charged particles emitted at midrapidity in Heavy-Ion collisions at intermediate energies shows the strongest sensitivity to the Nuclear Equation of State (EoS) which has been observed up to now within a microscopic model. This dependence on the nuclear EoS is predicted by Quantum Molecular Dynamics (QMD) calculations [1] which show as well that the absorption or rescattering of in-plane emitted particles by the spectator matter is not the main reason for the EoS dependence of the elliptic flow at mid-rapidity but different density gradients (and therefore different forces) in the direction of the impact parameter (x-direction) as compared to the direction perpendicular to the reaction plan (y-direction), caused by the presence of the spectator matter. The stronger density gradient in y-direction accelerates the particles more and creates therefore a negative v2. When using a soft momentum dependent EoS, the QMD calculations reproduce the experimental results.

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

Influence of final-state radiation on heavy-flavour observables in pp collisions

The influence of final-state radiation (FSR) of heavy quarks on observables in high-energy proton-proton collisions is studied. The transverse momentum correlation of D and Dbar mesons, which have been emitted with an azimuthal difference angle close to 180 degrees, is identified as an observable which is sensitive to the FSR process. We demonstrate this by performing calculations with the EPOS3+HQ model and with the event generator Pythia 6. The initial symmetric pT = pT' correlation for back-to-back pairs does not completely vanish in EPOS3+HQ, neither for the final DDbar pairs nor for the ccbar pairs before hadronisation. Also a significant difference in the shape of the correlation distribution for EPOS3+HQ and Pythia 6 is observed. Therefore, particle correlations in pp data offer the possibility to study several aspects of energy loss in heavy-ion collisions.

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

Heavy-flavor production and medium properties in high-energy nuclear collisions - What next?

Open and hidden heavy-flavor physics in high-energy nuclear collisions are entering a new and exciting stage towards reaching a clearer understanding of the new experimental results with the possibility to link them directly to the advancement in lattice Quantum Chromo-dynamics (QCD). Recent results from experiments and theoretical developments regarding open and hidden heavy-flavor dynamics have been debated at the Lorentz Workshop "Tomography of the quark-gluon plasma with heavy quarks}, which was held in October 2016 in Leiden, the Netherlands. In this contribution, we summarize identified common understandings and developed strategies for the upcoming five years, which aim at achieving a profound knowledge of the dynamical properties of the quark-gluon plasma.

nucl-th↗
arXiv2016

Degrees of Freedom of the Quark Gluon Plasma, tested by Heavy Mesons

Heavy quarks (charm and bottoms) are one of the few probes which are sensitive to the degrees of freedom of a Quark Gluon Plasma (QGP), which cannot be revealed by lattice gauge calculations in equilibrium. Due to the rapid expansion of the QGP energetic heavy quarks do not come to an equilibrium with the QGP. Their energy loss during the propagation through the QGP medium depends strongly on the modelling of the interaction of the heavy quarks with the QGP quarks and gluons, i.e. on the assuption of the degrees of freedom of the plasma. Here we compare the results of different models, the pQCD based Monte-Carlo (MC@sHQ), the Dynamical Quasi Particle Model (DQPM) and the effective mass approach, for the drag force in a thermalized QGP and discuss the sensitivity of heavy quark energy loss on the properties of the QGP as well as on non-equilibrium dynamics

hep-ph↗
arXiv2015

Transport Theory from the Nambu-Jona-Lasinio Lagrangian

Starting from the (Polyakov-) Nambu-Jona-Lasinio Lagrangian, (P)NJL, we formulate a transport theory which allows for describing the expansion of a quark-antiquark plasma and the subsequent transition to the hadronic world --without adding any new parameter to the standard (P)NJL approach, whose parameters are fixed to vacuum physics. This transport theory can be used to describe ultrarelativistic heavy-ion reaction data as well as to study the (first-order) phase transition during the expansion of the plasma. (P)NJL predicts such a phase transition for finite chemical potentials. In this contribution we give an outline of the necessary steps to obtain such a transport theory and present first results.

hep-ph↗
arXiv2015

FRIGA, A New Approach To Identify Isotopes and Hypernuclei In N-Body Transport Models

We present a new algorithm to identify fragments in computer simulations of relativistic heavy ion collisions. It is based on the simulated annealing technique and can be applied to n-body transport models like the Quantum Molecular Dynamics. This new approach is able to predict isotope yields as well as hyper-nucleus production. In order to illustrate its predicting power, we confront this new method to experimental data, and show the sensitivity on the parameters which govern the cluster formation.

nucl-th↗