Abstract
Measurements are presented from proton–proton collisions at centre-of-mass energies of , 2.36 and 7 TeV recorded with the ATLAS detector at the LHC. Events were collected using a single-arm minimum-bias trigger. The charged-particle multiplicity, its dependence on transverse momentum and pseudorapidity and the relationship between the mean transverse momentum and charged-particle multiplicity are measured. Measurements in different regions of phase space are shown, providing diffraction-reduced measurements as well as more inclusive ones. The observed distributions are corrected to well-defined phase-space regions, using model-independent corrections. The results are compared to each other and to various Monte Carlo (MC) models, including a new AMBT1 pythia6 tune. In all the kinematic regions considered, the particle multiplicities are higher than predicted by the MC models. The central charged-particle multiplicity per event and unit of pseudorapidity, for tracks with pT>100 MeV, is measured to be 3.483±0.009(stat)±0.106 (syst) at and 5.630±0.003(stat)±0.169 (syst) at .
Highlights
Inclusive charged-particle distributions have been previously measured in pp and ppcollisions in a range of different centre-of-mass energies [1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17]
Several quantum chromodynamics (QCD)-inspired models have been developed to interpret them. These models are frequently cast into Monte Carlo (MC) simulations with free parameters that can be constrained by measurements such as minimum bias distributions. These measurements contribute to the understanding of soft QCD; they are important in the determination of biases on high- pT phenomena due to underlying events (UEs) and event pileup effects and are of growing importance for future Large Hadron Collider (LHC) physics
This paper reports on measurements of primary charged-particle multiplicity distributions pu0us.9ibnTlgiecVtaht.eioAfintr[√s1t ]s∼. =T1h90e0.9μreTbseu−Vl1tsothfaerdeasaatalmsropelcpeoreirsdseesndimtebidylaatrhtte√oAtshT=aLt A2u.sS3e6dexTfpoeeVrrtihwmehefienrrtesatttAh7eTTLtreAaVcSkamnredicn∼oinm7sutμrmubc-−bt1iioaanst setup differs significantly from that at the other energies, due to the silicon tracker (SCT) not being at nominal voltage
Summary
Inclusive charged-particle distributions have been previously measured in pp and ppcollisions in a range of different centre-of-mass energies [1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17]. Several quantum chromodynamics (QCD)-inspired models have been developed to interpret them These models are frequently cast into Monte Carlo (MC) simulations with free parameters that can be constrained by measurements such as minimum bias distributions. Events are rejected if they have a second vertex with four or more tracks14 After this cut, the fraction of events with more than one interaction in the same bunch crossing is measured to be about 0.1%; the residual effect is neglected. At the lower centre-of-mass energies, the rate of multiple interactions is lower and neglected
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