Nuclear effects on the transverse momentum spectra of charged particles in pPb collisions at a nucleon-nucleon center-of-mass energy of 5.02 TeV

Abstract

Transverse momentum spectra of charged particles are measured by the CMS experiment at the CERN LHC in pPb collisions at sqrt(s[NN]) = 5.02 TeV, in the range 0.4 < pt < 120 GeV and pseudorapidity abs(eta[CM]) < 1.8 in the proton-nucleon center-of-mass frame. For pt < 10 GeV, the charged-particle production is asymmetric about eta[CM] = 0, with smaller yield observed in the direction of the proton beam, qualitatively consistent with expectations from shadowing in nuclear parton distribution functions (nPDF). A pp reference spectrum at sqrt(s) = 5.02 TeV is obtained by interpolation from previous measurements at higher and lower center-of-mass energies. The pt distribution measured in pPb collisions shows an enhancement of charged particles with pt > 20 GeV compared to expectations from the pp reference. The enhancement is larger than predicted by perturbative quantum chromodynamics calculations that include antishadowing modifications of nPDFs.