Flavor hierarchy at the chemical freeze-out from UrQMD

Tom Reichert,Gabriele Inghirami,Marcus Bleicher

doi:10.1051/epjconf/202225910005

Abstract

We introduce a novel approach based on elastic and inelastic scattering rates to extract the hyper-surface of the chemical freeze-out from a hadronic transport simulation. We use the Ultra-relativistic Quantum Molecular Dynamics (UrQMD) model to extract the chemical freeze-out hyper-surface of pions and kaons in the energy range from Elab = 1:23A GeV to √SNN = 7.7 GeV. By employing a coarse-graining procedure, we can extract the local temperature T and baryo-chemical potential μB on the chemical freeze-out surface and compare them to results from statistical model analysis. We find good agreement between the pion chemical freeze-out line extracted from the simulation and the freeze-out line from the statistical model extracted from data. In addition the simulations also hint towards the existence of a flavor hierarchy similar to the one observed in recent lattice QCD calculations.

Highlights

There is an ongoing debate about whether the phase transition line is connected to the chemical freeze-out line, i.e. the stage at which flavor changing reactions cease and the chemical yields of the hadrons are fixed
We find good agreement between the pion chemical freeze-out line extracted from the simulation and the freeze-out line from the statistical model extracted from data
We aim to contribute to the discussion of the “flavor hierarchy” question by extracting the microscopic chemical freeze-out hyper-surface Σcμfo(xν) from a dynamical hadronic transport simulation without the need to fit measured particle yield

Summary

Introduction

There is an ongoing debate about whether the phase transition line is connected to the chemical freeze-out line, i.e. the stage at which flavor changing reactions cease and the chemical yields of the hadrons are fixed. On the one hand there is the thermal model utilizing a relativistic hadron gas described by a volume (V), a temperature (T ) and the chemical potentials (μi) which successfully describes final state hadron yields over a broad range energies [1]. This finding is usually interpreted as thermal/chemical equilibrium being formed via statistical hadronization from the Quark-Gluon-Plasma (QGP). On the other hand there are ab initio lattice calculations investigating the temperature dependence of susceptibility ratios pointing towards a separation in the chemical decoupling temperatures of light and strange quarks [2,3,4]. We employ a coarse-graining procedure to infer the local temperature and baryo-chemical potential

Modeling chemical freeze-out in UrQMD

Results

Freeze-out of pions versus kaons

Thermodynamics on the hyper-surface

Summary