Nuclear effects on the transverse momentum spectra of charged particles in pPb collisions at√s_NN = 5.02 TeV

Transverse momentum spectra of charged particles are measured by the CMS experiment at the CERN LHC in pPb collisions at √s_NN = 5.02 TeV, in the range 0.4 < p_T < 120 GeV/c and pseudorapidity |η_cm| < 1.8 in the proton–nucleon center-of-mass frame. For p_T < 10 GeV/c, the charged-particle production is asymmetric about η_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 √s = 5.02 TeV is obtained by interpolation from previous measurements at higher and lower center-of-mass energies. The p_T distribution measured in pPb collisions shows an enhancement of charged particles with p_T > 20 GeV/c compared to expectations from the pp reference. The enhancement is larger than predicted by perturbative quantum chromodynamics calculations that include antishadowing modifications of nPDFs.