The forthcoming LHC measurement of the hadron multiplicity in proton-nucleus collisions is a crucial test of the $k_t$ factorization and gluon saturation based models. Here, we provide quantitative predictions for the pseudorapidity distribution of charged particles produced in minimum-bias proton-nucleus collisions at the LHC based on the idea of gluon saturation in the color glass condensate framework. Our formulation gives good descriptions of the LHC and the Relativistic Heavy Ion Collider (RHIC) data for the charged hadron multiplicities in both proton-proton and nucleus-nucleus collisions, and also the deep inelastic scattering in the Hadron Electron Ring Accelerator (HERA) at small Bjorken-$x$.

• Received 10 November 2011

DOI:https://doi.org/10.1103/PhysRevD.85.014028