Study of QCD dynamics using small systems

TL;DR

This study investigates QCD-related thermodynamic properties in small $p+p$ collision systems at high energy, finding signs of possible thermalization and limitations of current models in explaining observed phenomena.

Contribution

It provides evidence of a threshold in multiplicity indicating thermalization in small systems and compares experimental data with PYTHIA8, highlighting its inadequacy.

Findings

Threshold in multiplicity where thermodynamic quantities plateau

PYTHIA8 fails to reproduce key features of the data

Finite size effects do not fully explain particle spectra

Abstract

The multiplicity, finite system size and collision energy dependencies of heat capacity ($C_V$), conformal symmetry breaking measure (CSBM) and speed of sound ($c_s$) have been investigated using ALICE data for $p+p$ collisions at $\sqrt{s}$ = 7 TeV. The aim of this study is to ascertain the possibility of formation of a thermalized medium in such collisions. We find that there is a threshold in charged particle multiplicity beyond which $C_V$, CSBM and $c_s$ attain plateau. The presence of such threshold in multiplicity is further reflected in the variation of these quantities with center-of-mass energy ($\sqrt{s_{NN}}$). In order to have a grasp on experimentally obtained results, variation of $\langle p_T \rangle$ with multiplicity has also been studied. The experimental results have been contrasted with PYTHIA8 and it is found that PYTHIA8 is inadequate to explain the features reflected in these quantities, thereby indicating the possibility of thermalization in such small system. It is also observed that the finite size effects alone cannot explain the non-extensive nature of particle spectra in $p+p$ collisions.