Saturation and geometrical scaling

Michal Praszalowicz

doi:10.1051/epjconf/201714105005

Abstract

We discuss emergence of geometrical scaling as a consequence of the nonlinear evolution equations of QCD, which generate a new dynamical scale, known as the saturation momentum: Qs. In the kinematical region where no other energy scales exist, particle spectra exhibit geometrical scaling (GS), i.e. they depend on the ratio pT=Qs, and the energy dependence enters solely through the energy dependence of the saturation momentum. We confront the hypothesis of GS in different systems with experimental data.

Highlights

In this report we present a concise analysis of geometrical scaling (GS), slightly extended with respect to the presentation given at the XLVI International Symposium on Multiparticle Dynamics
Case, in the right panel where we plot R for λ = 0.32 no GS is seen. In this short note we have argued that geometrical scaling is clearly seen in the Deep inelastic scattering (DIS) and pp data
Phenomenological analysis analogical to the one described here has been used to look for the effects of GS in pA and heavy ion collisions and in pT correlation with multiplicity [2]–[5]

Summary

Introduction

In this report we present a concise analysis of GS, slightly extended with respect to the presentation given at the XLVI International Symposium on Multiparticle Dynamics. In QCD we have basically two sets of evolution equations that describe the change of parton densities with decreasing resolution scale 1/Q2 – DGLAP equations, or with growing energy (or equivalently with decreasing Bjorken x) – BFKL equation. In both cases the number of partons, or more precisely the number of gluons, is growing rapidly with the evolution variable. The travelling wave corresponds to the scaling solution with the saturation momentum given by Eq (1).

Inelastic pT spectra at the LHC

Electron-positron scattering

Summary