Multiplicity and mean transverse momentum of proton-proton collisions at √s = 900 GeV, 2.76 and 7 TeV with ALICE at the LHC

The charged particle multiplicity is measured for inelastic and non-single-diffractive proton-proton collisions at collision energies of 900 GeV, 2760 GeV and 7000 GeV. The data analysed corresponds to an integrated luminosity of 0.152 \(\pm\) 0.003 pb\(^{-1}\), 1.29 \(\pm\) 0.07 pb\(^{-1}\) and 2.02 \(\pm\) 0.12 pb\(^{-1}\) for each respective collision energy. The average transverse momentum per event as a function of charged multiplicity, for tracks with transverse momentum above 150 MeV/c and 500 MeV/c, is measured for inelastic proton-proton collisions. Two methods of deconvolution were studied, and an iterative method was used to correct the multiplicity distributions. The effect of pileup on multiplicity measurements was modelled using a toy Monte Carlo. The results presented extend the previous measurements made by ALICE to more than ten times the average charged multiplicity, and are compared to results from other experiments at similar energies, and to the Monte Carlo generators Phojet and the Perugia-0 tune of Pythia. The pseudorapidity density is estimated from the multiplicity distributions, and found to agree with other experimental results. The Phojet generator reproduces well the 900 GeV multiplicity distribution, but otherwise it and Pythia both underestimate the probability of higher multiplicities. The Pythia generator reproduces well the average transverse momentum distribution for tracks above 500 MeV/c, and overestimates the lower momentum distribution, while Phojet tends to underestimate the distribution for both momentum thresholds. Evidence of the violation of KNO scaling is shown for non-single-diffractive events in a pseudorapidity interval of \(\pm\)1, but not in \(\pm\)0.5.