ALICE measurements in p–Pb collisions: Charged particle multiplicity, centrality determination and implications for binary scaling

Measurements of particle production in proton–nucleus collisions provide a reference to disentangle final state effects, i.e. signatures of the formation of a deconfined hot medium, from initial state effects, already present in cold nuclear matter. Since many initial state effects are expected to vary as function of the number of collisions suffered by the incoming proton, it is crucial to estimate the centrality of the collision. In p-Pb collisions categorization of events into different centrality classes using a particle multiplicity distribution is complicated by the low particle multiplicities and the large multiplicity fluctuations. We present ALICE measurements of particle production in p-Pb collisions at √(s_NN)=5.02 TeV, including the pseudo-rapidity and transverse momentum dependence, and we discuss the event classification in centrality classes and its implications for the measurements of nuclear modification factors