Energy dependence of transverse momentum fluctuations in Pb+Pb collisions at the CERN Super Proton Synchrotron (SPS) at 20A to 158A GeV

TL;DR

This study measures event-by-event transverse momentum fluctuations in central Pb+Pb collisions across a range of energies at CERN SPS, finding no significant energy dependence or signs of critical point effects.

Contribution

It provides the first comprehensive analysis of $p_T$ fluctuations over multiple energies at SPS, comparing results with QCD predictions and models.

Findings

$p_T$ fluctuations are small and energy-independent.

No evidence of critical point effects in $p_T$ fluctuations.

Results align with UrQMD model predictions.

Abstract

Results are presented on event-by-event fluctuations of transverse momenta $p_T$ in central Pb+Pb interactions at 20$A$, 30$A$, 40$A$, 80$A$, and 158$A$ GeV. The analysis was performed for charged particles at forward center-of-mass rapidity ($1.1 < y^{*}_{\pi} < 2.6$). Three fluctuation measures were studied: the distribution of average transverse momentum - $M(p_T)$ - in the event, the $\Phi_{p_{T}}$ fluctuation measure and two-particle transverse momentum correlations. Fluctuations of $p_T$ are small and show no significant energy dependence in the energy range of the CERN Super Proton Synchrotron. Results are compared with QCD-inspired predictions for the critical point, and with the UrQMD model. Transverse momentum fluctuations, similar to multiplicity fluctuations, do not show the increase expected for freeze-out near the critical point of QCD.