Violation of Geometrical Scaling in pp Collisions at NA61/SHINE

TL;DR

This paper investigates geometrical scaling in negative pion production at NA61/SHINE energies, finding that while GS is expected, it is violated at low p_T and high Bjorken x due to nonperturbative effects and partonic structure changes.

Contribution

It provides an analysis of GS violation at low energies and identifies the conditions under which GS holds or breaks down in pp collisions.

Findings

GS approximately holds at certain energies and p_T ranges

Violation occurs at low p_T and high Bjorken x

Gluonic cloud dilution and quark effects cause deviations

Abstract

We analyze geometrical scaling (GS) of negative pion multiplicity p_T distributions at NA61/SHINE energies. We show that even though NA61/SHINE energies are low, one may expect to find GS in the particle spectra. We argue that qualitative behavior of ratios of multiplicities at different energies is in agreement with a simple picture of GS which is violated for p_T smaller than some nonperturbative scale Lambda and when larger Bjorken x of one of the scattering patrons crosses x_max above which gluonic cloud becomes dilute and quark degrees of freedom become important.