Event-by-event mean $p_{\rm T}$ fluctuations in pp and Pb-Pb collisions at the LHC

TL;DR

This study investigates event-by-event mean transverse momentum fluctuations in proton-proton and lead-lead collisions at the LHC, revealing dynamical correlations and collective effects, with results consistent across energies and system sizes.

Contribution

First comprehensive analysis of mean $p_T$ fluctuations in pp and Pb-Pb collisions at multiple energies using ALICE data, highlighting differences between peripheral and central collisions.

Findings

Dynamical fluctuations observed in all systems.

Fluctuation strength decreases in central Pb-Pb collisions.

Results align with models including collective phenomena.

Abstract

Event-by-event fluctuations of the mean transverse momentum of charged particles produced in pp collisions at $\sqrt{s}$ = 0.9, 2.76 and 7 TeV, and Pb-Pb collisions at $\sqrt{s_{NN}}$ = 2.76 TeV are studied as a function of the charged-particle multiplicity using the ALICE detector at the LHC. Dynamical fluctuations indicative of correlated particle emission are observed in all systems. The results in pp collisions show little dependence on collision energy. The Monte Carlo event generators PYTHIA and PHOJET are in qualitative agreement with the data. Peripheral Pb-Pb data exhibit a similar multiplicity dependence as that observed in pp. In central Pb-Pb, the results deviate from this trend, featuring a significant reduction of the fluctuation strength. The results in Pb--Pb are in qualitative agreement with previous measurements in Au-Au at lower collision energies and with expectations from models that incorporate collective phenomena.