Universality of the transverse momentum distributions in the framework of percolation of strings

Abstract

In the framework of percolation of color sources, the transverse momentum distribution in heavy ion and $p+p$ collisions at all centralities and energies are shown to follow a universal behaviour. The width of the distribution depends on the fluctuations of the number of color sources per cluster. At low densities, there are only independent single color sources, no fluctuations occurs and the distribution is described by a single exponential. At very high densities, only one cluster of many color sources appears and therefore there are not fluctuations either and the hardness of the distribution is suppressed. The Cronin effect in this framework is due to a maximum of the fluctuations which decreases as the density increases. We obtain a good agreement with experimental data including the low $p_T$ behaviour and the spectra for different particles. We show that the transverse momentum and multiplicity distributions are related to each other in a defined way. This point is satisfied by the experimental data on $p+p$ collisions at different energies.