Comparison of p−p, p−Pb , and Pb-Pb collisions in the thermal model: Multiplicity dependence of thermal parameters

Natasha Sharma,Masimba Paradza,Boris Hippolyte,Jean Cleymans

doi:10.1103/physrevc.99.044914

Abstract

% An analysis is made of the particle composition (hadrochemistry) of the final state in proton-proton (p-p), proton-lead (p-Pb) and lead-lead (Pb-Pb) collisions as a function of the charged particle multiplicity ($\dNchdeta$). The thermal model is used to determine the chemical freeze-out temperature as well as the radius and strangeness saturation factor $\gamma_s$. Three different ensembles are used in the analysis namely, the grand canonical ensemble, the canonical ensemble with exact strangeness conservation and the canonical ensemble with exact baryon number, strangeness and electric charge conservation. It is shown that for high multiplicities (at least 20 charged hadrons in the mid-rapidity interval considered) the three ensembles lead to the same results.

Highlights

In high-energy collisions, applications of the thermalstatistical model in the form of the hadron resonance gas model have been successful in describing the composition of the final state, e.g., the yields of pions, kaons, protons, and other hadrons
In this paper we have investigated three different ensembles to analyze the variation of particle yields with the multiplicity of charged particles produced√in the center-of-mass energy of s proton-proton collisions at = 7 TeV [27], p-Pb collisions at 5.02 TeV [28,29], and Pb-Pb collisions at 2.76 TeV
We have kept the basic structure of the thermal model as presented in Ref. [24] and focused on the resulting thermal parameters Tch, γs and the radius and their dependence on the final-state multiplicity

Summary

INTRODUCTION

In high-energy collisions, applications of the thermalstatistical model in the form of the hadron resonance gas model have been successful (see, e.g., Refs. [1,2] for two recent publications) in describing the composition of the final state, e.g., the yields of pions, kaons, protons, and other hadrons. [1,2] for two recent publications) in describing the composition of the final state, e.g., the yields of pions, kaons, protons, and other hadrons In these descriptions use is made of the grand canonical ensemble and the canonical ensemble with exact strangeness conservation. The use the K-matrix formalism to take interactions into account [23] These proposals improve the agreement with the observed yields and, some of them change the chemical freeze-out temperature Tch in only a minimal way, such as those presented recently in Refs. This agreement starts when there are at least 20 charged hadrons in the midrapidity interval being considered It throws doubt on the applicability of the thermal model as applied to p-p collisions with low multiplicity. The convergence of the results in the three ensembles lends support to the idea that one reaches a thermodynamic limit where the results are independent of the ensemble being used

ENSEMBLES CONSIDERED IN THE THERMAL MODEL

14 Grand Canonical Canonical S

COMPARISON OF DIFFERENT ENSEMBLES

DISCUSSION AND CONCLUSIONS