Low-Momentum Pion Enhancement from Schematic Hadronization of a Gluon-Saturated Initial State

Elizaveta Nazarova,David Blaschke,Łukasz Juchnowski,Tobias Fischer

doi:10.3390/particles2010010

Abstract

We study the particle production in the early stage of the ultrarelativistic heavy-ion collisions. To this end the Boltzmann kinetic equations for gluons and pions with elastic rescattering are considered together with a simple model for the parton-hadron conversion process (hadronisation). It is shown that the overpopulation of the gluon phase space in the initial state leads to an intermediate stage of Bose enhancement in the low-momentum gluon sector which due to the gluon-pion conversion process is then reflected in the final distribution function of pions. This pattern is very similar to the experimental finding of a low-momentum pion enhancement in the ALICE experiment at the CERN Large Hadron Collider (LHC). Relations to the thermal statistical model of hadron production and the phenomenon of thermal and chemical freeze-out are discussed in this context.

Highlights

One of the issues which can be addressed by the kinetic approach is the question of a low-momentum pion enhancement in heavy ion collisions [1]
An explanation linked to the presence of non-equilibrium physics and a precursor of pion condensation in heavy ion collisions should be the favorable one, especially after the recent analysis of particle correlations performed by the ALICE collaboration is showing a coherent fraction of charged π-meson emission that is reaching 23% [1,9]
An alternative scheme may rely on the Boltzmann kinetic equation for gluons and pions with elastic rescattering and a simple model for the parton-hadron conversion process

Summary

Introduction

One of the issues which can be addressed by the kinetic approach is the question of a low-momentum pion enhancement in heavy ion collisions [1]. An explanation linked to the presence of non-equilibrium physics and a precursor of pion condensation in heavy ion collisions should be the favorable one, especially after the recent analysis of particle correlations performed by the ALICE collaboration is showing a coherent fraction of charged π-meson emission that is reaching 23% [1,9]. Such formation of a Bose condensate is usually described by the introduction of additional non-equilibrium parameters to the statistical approach [10,12], see [2,8,13]. We demonstrate the evolution of the coupled gluon and pion distribution functions in this case within a schematic model of coupled kinetic equations

Kinetic Equation Approach to Thermalization and Hadronization

Results

Discussion