Particle multiplicities in the central region of high-energy collisions from $k_T$-factorization with running coupling corrections

Abstract

Horowitz and Kovchegov have derived a $k_T$-factorization formula for particle production at small $x$ which includes running coupling corrections. We perform a first numerical analysis to confront the theory with data on the energy and centrality dependence of particle multiplicities at midrapidity in high-energy p+A (and A+A) collisions. Moreover, we point out a strikingly different dependence of the multiplicity per participant on $N_{\text{part}}$ in p+Pb vs.\ Pb+Pb collisions at LHC energies, and argue that the observed behavior follows rather naturally from the convolution of the gluon distributions of an asymmetric vs. symmetric projectile and target.

arXiv comment8 pages, 8 figures; v3: 2 new figures, matches the version accepted by Physics Letters B

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