Measurement of charged particle multiplicities in $pp$ collisions at ${\sqrt{s} =7}$TeV in the forward region

TL;DR

This paper measures charged particle multiplicities in proton-proton collisions at 7 TeV in the forward region using the LHCb detector, revealing that existing models underestimate particle production.

Contribution

First measurement of charged particle multiplicities in the forward region at 7 TeV with detailed comparison to event generators.

Findings

Models underestimate charged particle production.

Data provides new constraints for QCD models.

Charged particle density varies with pseudorapidity.

Abstract

The charged particle production in proton-proton collisions is studied with the LHCb detector at a centre-of-mass energy of ${\sqrt{s} =7}$TeV in different intervals of pseudorapidity $\eta$. The charged particles are reconstructed close to the interaction region in the vertex detector, which provides high reconstruction efficiency in the $\eta$ ranges $-2.5<\eta<-2.0$ and $2.0<\eta<4.5$. The data were taken with a minimum bias trigger, only requiring one or more reconstructed tracks in the vertex detector. By selecting an event sample with at least one track with a transverse momentum greater than 1 GeV/c a hard QCD subsample is investigated. Several event generators are compared with the data; none are able to describe fully the multiplicity distributions or the charged particle density distribution as a function of $\eta$. In general, the models underestimate the charged particle production.