# Thermalization in small system of hadron gas and high-multiplicity pp events

## TL;DR

This paper investigates how the degree of thermalization, measured by the Knudsen number, varies with system size in hadron gases, supporting the use of hydrodynamics in interpreting high-multiplicity proton-proton collision events.

## Contribution

It provides a comparative analysis of Knudsen numbers in heavy-ion and proton-proton collisions, extending thermalization studies to small systems.

## Key findings

- Hydrodynamics is applicable to high-multiplicity pp events.
- Knudsen numbers in small systems are similar to those in heavy-ion collisions.
- Supports thermalization in small hadron systems.

## Abstract

We study the system-size dependence of Knudsen number, a measure of degree of thermalization, for hadron resonance gas that follows the Lattice-QCD equation of state at zero chemical potential. A comparison between Knudsen numbers for the AuAu collisions at RHIC and the hadron gas of size similar to the size of high-multiplicity pp events at LHC, reassures the applicability of hydrodynamics in interpreting the features of particle production in high-multiplicity pp events.