Abstract: | Charged-particle production was studied in proton-proton collisions collected
at the LHC with the ALICE detector at centre-of-mass energies 0.9 TeV and 2.36
TeV in the pseudorapidity range |eta| < 1.4. In the central region (|eta| <
0.5), at 0.9 TeV, we measure charged-particle pseudorapidity density dNch/deta
= 3.02 +- 0.01 (stat.) +0.08 -0.05 (syst.) for inelastic interactions, and
dNch/deta = 3.58 +- 0.01 (stat.) +0.12 -0.12 (syst.) for non-single-diffractive
interactions. At 2.36 TeV, we find dNch/deta = 3.77 +- 0.01 (stat.) +0.25 -0.12
(syst.) for inelastic, and dNch/deta = 4.43 +- 0.01 (stat.) +0.17 -0.12 (syst.)
for non-single-diffractive collisions. The relative increase in
charged-particle multiplicity from the lower to higher energy is 24.7% +- 0.5%
(stat.) +5.7% -2.8% (syst.) for inelastic and 23.7% +- 0.5% (stat.) +4.6% -1.1%
(syst.) for non-single-diffractive interactions. This increase is consistent
with that reported by the CMS collaboration for non-single-diffractive events
and larger than that found by a number of commonly used models. The
multiplicity distribution was measured in different pseudorapidity intervals
and studied in terms of KNO variables at both energies. The results are
compared to proton-antiproton data and to model predictions. |