Forward particle production in proton-nucleus collisions at next-to-leading order

TL;DR

This paper presents a next-to-leading order calculation of forward particle production in proton-nucleus collisions within the Color Glass Condensate framework, introducing a new factorization scheme that avoids unphysical results.

Contribution

It introduces a novel factorization scheme for NLO calculations in the CGC framework that eliminates rapidity subtraction and ensures physically meaningful cross sections.

Findings

NLO corrections are of the expected size.

The new scheme produces positive, well-defined cross sections.

Avoids fine-tuning issues of previous approaches.

Abstract

We consider the next-to-leading order (NLO) calculation of single inclusive particle production at forward rapidities in proton-nucleus collisions and in the framework of the Color Glass Condensate (CGC). We focus on the quark channel and the corrections associated with the impact factor. In the first step of the evolution the kinematics of the emitted gluon is kept exactly (and not in the eikonal approximation), but such a treatment which includes NLO corrections is not explicitly separated from the high energy evolution. Thus, in this newly established "factorization scheme", there is no "rapidity subtraction". The latter suffers from fine tuning issues and eventually leads to an unphysical (negative) cross section. On the contrary, our reorganization of the perturbation theory leads by definition to a well-defined cross section and the numerical evaluation of the NLO correction is shown to have the correct size.