Multiplicity in pp and AA collisions: the same power law from energy-momentum constraints in string production

We show that the dependence of the charged particle multiplicity on the centre-of-mass energy of the collision is, in the String Percolation Model, driven by the same power law behavior in both proton-proton and nucleus- nucleus collisions. The observed different growths are a result of energy- momentum constraints that limit the number of formed strings at low en- ergy. Based on the very good description of the existing data, we provide predictions for future high energy LHC runs.