Opacity estimation of OO collision from CoMBolt-ITA hybrid

TL;DR

This paper uses the CoMBolt-ITA hybrid model to analyze opacity in OO collisions at the LHC, revealing that larger centrality OO collisions tend to deviate from fluid-like behavior.

Contribution

It introduces a detailed modeling approach to estimate the opacity of OO collisions, enhancing understanding of system size effects in heavy-ion physics.

Findings

OO collisions with centralities >60% show reduced fluid-like behavior

The hybrid model effectively describes initial state and evolution stages

Data-model comparison suggests a transition from high to low opacity regimes

Abstract

Understanding the effect of system size on the applicability of the hydrodynamic description in heavy-ion physics remains unclear. Recent measurements of OO collisions at the LHC offer a new opportunity to refine our understanding of collectivity because of their intermediate size relative to heavy-ion and small-system collisions, as well as the relatively good control over their initial state. We use the CoMBolt-ITA hybrid model to describe recent OO measurements at the LHC. The model employs TrENTo for the initial state. A combination of the pre-equilibration and hydrodynamized medium stages is modeled consistently by CoMBolt-ITA, which evolves the Boltzmann distribution of massless collective excitations. The afterburner stage is included by employing UrQMD. Using this approach, we test whether the system lies in the regime where its spatial size approaches the mean free path, corresponding to low opacity, or in the opposite limit, where its size exceeds the mean free path sufficiently to enter the fluid-like evolution regime with high opacity. We find that, in light of the data-model comparison and considering the current status of the model, OO collisions with centralities larger than $60\%$ gradually leave the domain of fluid-like evolution.