  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.
