Transverse-momentum and pseudorapidity distributions of charged hadrons in pp collisions at sqrt(s) = 7 TeV

TL;DR

This paper reports measurements of charged-hadron transverse-momentum and pseudorapidity distributions in proton-proton collisions at 7 TeV, revealing higher multiplicities than models predict and providing insights into particle production at high energies.

Contribution

First measurement of charged-hadron distributions at 7 TeV using multiple reconstruction methods in CMS, highlighting discrepancies with theoretical models.

Findings

Charged-particle multiplicity per unit pseudorapidity is 5.78.

Relative increase in multiplicity from 0.9 to 7 TeV is 66.1%.

Mean transverse momentum is 0.545 GeV/c.

Abstract

Charged-hadron transverse-momentum and pseudorapidity distributions in proton-proton collisions at sqrt(s) = 7 TeV are measured with the inner tracking system of the CMS detector at the LHC. The charged-hadron yield is obtained by counting the number of reconstructed hits, hit-pairs, and fully reconstructed charged-particle tracks. The combination of the three methods gives a charged-particle multiplicity per unit of pseudorapidity, dN(charged)/d(eta), for |eta| < 0.5, of 5.78 +/- 0.01 (stat) +/- 0.23 (syst) for non-single-diffractive events, higher than predicted by commonly used models. The relative increase in charged-particle multiplicity from sqrt(s) = 0.9 to 7 TeV is 66.1% +/- 1.0% (stat) +/- 4.2% (syst). The mean transverse momentum is measured to be 0.545 +/- 0.005 (stat) +/- 0.015 (syst) GeV/c. The results are compared with similar measurements at lower energies.