  The ATLAS experiment at the LHC has measured the centrality dependence of
charged particle pseudorapidity distribution, charged particle spectra, and the
two-particle correlations in p+Pb collisions at a nucleon-nucleon
centre-of-mass energy of sqrt(s_NN)=5.02TeV. Charged particles were measured
over |eta|<2.7 using the ATLAS detector tracking system. The p+Pb collision
centrality was characterized by the total transverse energy deposited over the
interval 3.2<eta<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 eta 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 p_T.
