Transverse momentum spectra of charged particles are measured by the CMS experiment at the CERN LHC in pPb collisions at (Formula Presented.), in the range $$0.4 < pT < 120GeV/c and pseudorapidity (Formula Presented.) in the proton–nucleon center-of-mass frame. For (Formula Presented.), the charged-particle production is asymmetric about (Formula Presented.), 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 (Formula Presented.) is obtained by interpolation from previous measurements at higher and lower center-of-mass energies. The (Formula Presented.) distribution measured in pPb collisions shows an enhancement of charged particles with (Formula Presented.) compared to expectations from the pp reference. The enhancement is larger than predicted by perturbative quantum chromodynamics calculations that include antishadowing modifications of nPDFs.
- Relativistic heavy-ion collisions