Event-by-event mean p_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 energy independence in pp and peripheral Pb-Pb, but significant fluctuation reduction in central Pb-Pb collisions.

Contribution

It provides the first detailed analysis of mean p_T fluctuations across different collision systems and energies, highlighting differences in fluctuation behavior between pp and Pb-Pb collisions.

Findings

Dynamical fluctuations observed beyond statistical expectations in both systems.

No significant energy dependence of fluctuations in pp and peripheral Pb-Pb collisions.

Central Pb-Pb collisions show a notable reduction in fluctuations.

Abstract

The ALICE detector at the LHC is used to study the properties of the Quark-Gluon Plasma produced in heavy-ion collisions. As a reference measurement, also the analysis of proton-proton (pp) collisions is very important. In the study presented here, event-by-event fluctuations of the mean transverse momentum are analysed in pp collisions at sqrt(s) = 0.9, 2.76 and 7 TeV, and Pb-Pb collisions at sqrt(s_NN) = 2.76 TeV as a function of the charged-particle multiplicity. In both systems, dynamical fluctuations beyond the statistical expectation are observed. In pp collisions, no significant dependence on collision energy is found, even in comparison to inclusive results at much lower collision energies. Likewise, central A-A collisions show only little dependence on collision energy. The multiplicity dependence observed in peripheral Pb-Pb data is in agreement with that in pp collisions. Going to more central Pb-Pb collisions, a clear deviation from this trend is found, reaching a significant reduction of the fluctuations in most central collisions. Comparisons to Monte Carlo event generators show good agreement in pp, but rather large differences in Pb-Pb collisions.