Centrality Dependence of the Balance Functions for Identified Particles in Pb--Pb Collisions Using Pythia + Angantyr

TL;DR

This study uses PYTHIA 8.3 + Angantyr to analyze the centrality dependence of balance functions for identified particles in Pb--Pb collisions, revealing differences in correlation widths and model limitations.

Contribution

It provides the first detailed analysis of balance functions for pions, kaons, and protons in Pb--Pb collisions using PYTHIA + Angantyr, highlighting model performance and resonance effects.

Findings

Pion balance functions are narrower than kaons and protons.

Pion balance function width decreases from peripheral to central collisions.

PYTHIA + Angantyr describes peripheral but not central Pb--Pb data well.

Abstract

In this paper, we study the balance functions for pions, kaons, and protons in Pb--Pb collisions at $\sqrt{s_{\mathrm{NN}}} = 2.76$ TeV using the PYTHIA 8.3 + Angantyr model. The balance function is evaluated through two-particle azimuthal angular correlations $(\Delta \phi, \Delta \eta)$ between particle and antiparticle. Correlations are constructed for $\pi\pi$, $KK$, and $pp$, and their dependence on collision centrality is investigated. The results indicate that the balance function for pions is narrower compared to kaons and protons. Notably, the pion balance function width decreases from peripheral to central collisions, while the widths for kaons and protons remain nearly unchanged. For the Monash 2013 tune used in this study, PYTHIA 8.3 + Angantyr describes peripheral collisions reasonably well but does not quantitatively reproduce central Pb--Pb data. This suggests that an improved description of central Pb--Pb collisions may require a dedicated heavy-ion tuning of the Angantyr framework. We further explore the influence of resonance decays and collective effects by incorporating multi-parton interactions and color reconnection into the analysis. Owing to resonance effects and Bose--Einstein correlations, a dip at $\Delta \eta = 0$ and $\Delta \phi = 0$ is observed for pions and kaons.