Nuclear effects on the transverse momentum spectra of charged particles in pPb collisions at $\sqrt{s_{\mathrm{NN}}}$ = 5.02 TeV

Abstract

Transverse momentum spectra of charged particles are measured by the CMS experiment at the CERN LHC in pPb collisions at $\sqrt{s_{\mathrm{NN}}}$ = 5.02 TeV, in the range of $p_\mathrm{T}$ between 0.4 and 120 GeV/$c$ and pseudorapidity $|\eta_\mathrm{CM}|$ lower than 1.8 in the proton-nucleon center-of-mass frame. For $p_\mathrm{T}$ lower than 10 GeV/$c$, the charged-particle production is asymmetric about $|\eta_\mathrm{CM}|$ = 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 $p_\mathrm{T}$ distribution measured in pPb collisions shows an enhancement of charged particles with $p_\mathrm{T}$ larger than 20 GeV/$c$ compared to expectations from the pp reference. The enhancement is larger than predicted by perturbative quantum chromodynamic calculations that include antishadowing modifications of nPDFs