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

Transverse momentum spectra of charged particles are measured by the CMS experiment at the CERN LHC in pPb collisions at s NN − − − √ =5.02 sNN=5.02 TeV TeV , in the range 0.4<p T <120 0.4<pT<120 GeV/c GeV/c and pseudorapidity |η CM |<1.8 |ηCM|<1.8 in the proton–nucleon center-of-mass frame. For p T <10 pT<10 GeV/c GeV/c , the charged-particle production is asymmetric about η CM =0 ηCM=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 s=5.02 TeV TeV is obtained by interpolation from previous measurements at higher and lower center-of-mass energies. The p T pT distribution measured in pPb collisions shows an enhancement of charged particles with p T >20 pT>20 GeV/c 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