Particle production and long-range correlations in p+Pb collisions with the ATLAS detector

The ATLAS experiment at the LHC has measured the centrality dependence of charged-particle pseudorapidity distribution, charged-particle spectra, and two-particle correlations in p+Pb collisions at a nucleon–nucleon centre-of-mass energy of sNN=5.02 TeV . Charged particles were measured over |η|<2.7 using the ATLAS detector tracking system. The p+Pb collision centrality was characterised by the total transverse energy deposited over the interval 3.2<η<4.9 in the direction of the Pb-beam. Three different calculations of the number of participating nucleons have been carried out using a standard Glauber initial-state model as well as two Glauber–Gribov extensions. Charged-particle multiplicities per participant pair, and the normalised charged-particle spectra are found to vary in shape with η and also with the model, pointing to the importance of the fluctuating nature of nucleon–nucleon collisions in the modelling of the initial state of p+Pb collisions. The two-particle correlation exhibits flow-like modulations for all centrality intervals and particle pT .