Measurement of the Nuclear Modification Factor and Prompt Charged Particle Production in p-Pb and pp Collisions at SQRT(SNN) =5 TeV

Abstract

The production of prompt charged particles in proton–lead collisions and in proton–proton collisions at the nucleon–nucleon center-of-mass energy SQRT(sNN) = 5 TeV is studied at LHCb as a function of pseudorapidity (eta) and transverse momentum (pT) with respect to the proton beam direction. The nuclear modification factor for charged particles is determined as a function of eta between -4.8 < eta < -2.5 (backward region) and 2.0 < eta < 4.8 (forward region), and pT between 0.2 < pT < 8.0 GeV/c. The results show a suppression of charged particle production in proton–lead collisions relative to proton–proton collisions in the forward region and an enhancement in the backward region for pT larger than 1.5 GeV/c. This measurement constrains nuclear PDFs and saturation models at previously unexplored values of the parton momentum fraction down to 10^-6.