Measurement of event-by-event transverse momentum and multiplicity fluctuations using strongly intensive measures $\Delta[P_T, N]$ and $\Sigma[P_T, N]$ in nucleus-nucleus collisions at the CERN Super Proton Synchrotron

TL;DR

This paper reports on measurements of event-by-event transverse momentum and multiplicity fluctuations in nucleus-nucleus collisions at CERN SPS, using strongly intensive measures, revealing system size dependence but no significant energy dependence.

Contribution

It extends previous NA49 fluctuation studies by analyzing the strongly intensive measures $ ext{Δ}[P_T, N]$ and $ ext{Σ}[P_T, N]$, providing new insights into fluctuation behavior across different system sizes.

Findings

Fluctuations show no significant energy dependence within SPS range.

Largest fluctuation values observed in peripheral Pb+Pb collisions.

Results compared with NA61/SHINE data and theoretical models.

Abstract

Results from the NA49 experiment at the CERN SPS are presented on event-by-event transverse momentum and multiplicity fluctuations of charged particles, produced at forward rapidities in central Pb+Pb interactions at beam momenta 20$A$, 30$A$, 40$A$, 80$A$, and 158$A$ GeV/c, as well as in systems of different size ($p+p$, C+C, Si+Si, and Pb+Pb) at 158$A$ GeV/c. This publication extends the previous NA49 measurements of the strongly intensive measure $\Phi_{p_T}$ by a study of the recently proposed strongly intensive measures of fluctuations $\Delta[P_T, N]$ and $\Sigma[P_T, N]$. In the explored kinematic region transverse momentum and multiplicity fluctuations show no significant energy dependence in the SPS energy range. However, a remarkable system size dependence is observed for both $\Delta[P_T, N]$ and $\Sigma[P_T, N]$, with the largest values measured in peripheral Pb+Pb interactions. The results are compared with NA61/SHINE measurements in $p+p$ collisions, as well as with predictions of the UrQMD and EPOS models.