Why mean $p_{\rm T}$ is interesting

Abstract

We discuss energy dependence of mean $p_{\rm T}$ correlation with $N_{\rm ch}$ basing on general features of high energy collisions such as saturation and geometrical scaling. We use Color Glass Condensate calculation of an effective interaction radius that scales as a third root of multiplicity, and then saturates. With this model input we construct scaling variable for $< p_{\rm T} > (N_{\rm ch})$ at different energies both for pp and pPb collisions, and show that recent ALICE data indeed does exhibit this scaling property. We discuss energy dependence of the interaction radius and argue that since the radius cannot grow too large, a universal behavior of $< p_{\rm T} >$ for large multiplicities is expected.