Centrality dependence of charged particle production in proton–lead collisions measured by ATLAS

Abstract

The ATLAS experiment at the LHC has measured the centrality dependence of charged particle pseudorapidity distributions, d N ch / d η , in p + Pb collisions at a nucleon–nucleon center-of-mass energy of s NN = 5.02 TeV . Charged particles were reconstructed over | η | < 2.7 using the ATLAS pixel detector. The proton–lead collision centrality was characterized by the total transverse energy measured over the pseudorapidity interval 3.1 < η < 4.9 in the direction of the lead beam. Three different calculations of the number of participants, N part , have been carried out using a standard Glauber model as well as two Glauber–Gribov extensions, providing results pointing to the importance of the fluctuating nature of nucleon–nucleon collisions in the modeling of the initial state of p + Pb collisions.