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

The ATLAS experiment at the LHC has measured the centrality dependence of charged particle pseudorapidity distributions, dNch/dηdNch/dη, in p+Pbp+Pb collisions at a nucleon–nucleon center-of-mass energy of sNN=5.02 TeV. Charged particles were reconstructed over |η|<2.7|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<4.93.1<η<4.9 in the direction of the lead beam. Three different calculations of the number of participants, NpartNpart, 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+Pbp+Pb collisions.