Higher-order transverse momentum fluctuations in heavy-ion collisions

TL;DR

This paper develops a framework to analyze higher-order transverse momentum fluctuations in heavy-ion collisions, revealing power-law behaviors and differences across collision systems, serving as a baseline for future studies.

Contribution

It introduces a validated method to calculate $p_T$ fluctuations up to 4th order using standard and subevent techniques, accounting for initial state fluctuations.

Findings

Power-law dependence of cumulants on charged particle multiplicity.

Larger fluctuations in $pp$ collisions compared to $p$+Pb and Pb+Pb at same $N_{ch}$.

Short-range correlations are suppressed in subevent method.

Abstract

In relativistic heavy-ion collisions, the event-by-event mean transverse momentum fluctuations are sensitive to overlap area and energy density fluctuations in initial state. We present a framework to calculate $p_{\mathrm{T}}$ fluctuations up to $4^{\mathrm{th}}$-order using standard and subevent methods, which is validated using the HIJING model. We observe a power-law dependence for cumulants of all orders as a function of charged particle multiplicity $N_{\mathrm{ch}}$, consistent with a simple independent source picture. The fluctuation in $pp$ collisions is observed to be larger than for $p+$Pb, Pb+Pb and Xe+Xe collisions at the same $N_{\mathrm{ch}}$ due to bias in number of contributing sources. The short-range correlations are greatly suppressed in subevent method in comparison to calculations based on the standard method. This study provides a baseline for transverse momentum fluctuations without the presence of final state effects.