Geometric Scaling at RHIC and LHC

TL;DR

This paper introduces a phenomenological model showing that RHIC data for hadron production align with geometric scaling, similar to small-x DIS data, and discusses how LHC measurements can test the evolution of the anomalous dimension gamma.

Contribution

The paper develops a new dipole scattering amplitude model demonstrating geometric scaling at RHIC and proposes LHC measurements to test small-x evolution effects on gamma.

Findings

RHIC data are compatible with geometric scaling.

LHC predictions show sensitivity to gamma variation.

Proposes using transverse momentum fall-off to test small-x evolution.

Abstract

We present a new phenomenological model of the dipole scattering amplitude to demonstrate that the RHIC data for hadron production in d-Au collisions for all available rapidities are compatible with geometric scaling, just like the small-x inclusive DIS data. A detailed comparison with earlier geometric scaling violating models of the dipole scattering amplitude in terms of an anomalous dimension gamma is made. In order to establish whether the geometric scaling violations expected from small-x evolution equations are present in the data a much larger range in transverse momentum and rapidity must be probed. Predictions for hadron production in p-Pb and p-p collisions at LHC are given. We point out that the fall-off of the transverse momentum distribution at LHC is a sensitive probe of the variation of gamma in a region where x is much smaller than at RHIC. In this way, the expectation for the rise of gamma from small-x evolution can be tested.