Gluon saturation and energy dependence of hadron multiplicity in pp and AA collisions at the LHC

TL;DR

This paper explains the different energy dependence of hadron multiplicity in proton-proton and lead-lead collisions at the LHC using gluon saturation and angular-ordering effects in the Color-Glass-Condensate framework.

Contribution

It introduces a novel approach incorporating angular-ordering in gluon decay cascades within the saturation model to explain LHC collision data.

Findings

Good agreement with LHC data for p+p and Pb+Pb collisions

Different energy dependence explained by saturation effects

Angular-ordering enhances model accuracy in nucleus-nucleus collisions

Abstract

The recent results in \sqrt{s}=2.76 TeV Pb+Pb collisions at the Large Hadron Collider (LHC) reported by the ALICE collaboration shows that the power-law energy-dependence of charged hadron multiplicity in Pb+Pb collisions is significantly different from p+p collisions. We show that this different energy-dependence can be explained by inclusion of a strong angular-ordering in the gluon-decay cascade within the Color-Glass-Condensate (or gluon saturation) approach. This effect is more important in nucleus-nucleus collisions where the saturation scale is larger than 1 GeV. Our prescription gives a good description of the LHC data both in p+p and Pb+Pb collisions.