Longitudinal boost-invariance of charge balance function in hadron-hadron and nucleus-nucleus collisions

TL;DR

This study demonstrates that the charge balance function remains invariant along the longitudinal direction in both hadron-hadron and nucleus-nucleus collisions within certain models, aligning with experimental observations.

Contribution

It provides a detailed analysis of the boost-invariance of the charge balance function using Monte Carlo simulations, highlighting model-dependent behaviors and physical implications.

Findings

Charge balance function is boost-invariant in PYTHIA and AMPT default models.

Scaling by pseudorapidity window width makes the balance function independent of window size.

Boost-invariance is violated in AMPT with string melting.

Abstract

Using Monte Carlo generators of the PYTHIA model for hadron-hadron collisions and a multi-phase transport (AMPT) model for nucleus-nucleus collisions, the longitudinal boost-invariance of charge balance function and its transverse momentum dependence are carefully studied. It shows that the charge balance function is boost-invariant in both {\it p}+{\it p} and Au+Au collisions in these two models, consistent with experimental data. The balance function properly scaled by the width of the pseudorapidity window is independent of the position or the size of the window and is corresponding to the balance function of the whole pseudorapidity range. This longitudinal property of balance function also holds for particles in small transverse momentum ranges in the PYTHIA and the AMPT default models, but is violated in the AMPT with string melting. The physical origin of the results are discussed.