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

TL;DR

This paper reports on measurements of charged particle transverse momentum spectra in proton-lead collisions at 5.02 TeV, revealing nuclear effects such as shadowing and an unexpected high-pt enhancement beyond current theoretical predictions.

Contribution

First measurement of charged particle spectra in pPb collisions at 5.02 TeV covering a wide pt range, highlighting nuclear modifications and discrepancies with existing models.

Findings

Smaller yield of low-pt particles in proton direction due to shadowing.

Observed high-pt enhancement exceeds predictions from current nPDF models.

Asymmetry in particle production consistent with nuclear effects.

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.