Event-by-event mean pT fluctuations in pp and Pb–Pb collisions at the LHC

Abstract

Event-by-event fluctuations of the mean trans- verse momentum of charged particles produced in pp colli- sions at √s = 0.9, 2.76 and 7 TeV, and Pb–Pb collisions at √sNN = 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 emis- sion 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 sim- ilar multiplicity dependence as that observed in pp. In central Pb–Pb, the results deviate from this trend, featuring a signif- icant 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.