Multiplicity distributions in rapidity for Pb-Pb and p-Pb central collisions from a simple model

In the String Percolation Model [1] the particle density is proportional, once the colour reduction factor is taken into account, to the average number of participants ρ ∝ NA; the normalized particle density at mid-rapidity is related to the gluon distribution at small Bjorken-x, ρ ∝ exp ; and the dense-dilute separation scale decreases, from energy conservation, linearly with Y , ∆0 = −αY with 0 < α < 1. Rewriting (2) in rapidity ρ ≡ dN dy = NA · e e |y|−(1−α)Y δ + 1 . (3)