# Forward particle production in proton-nucleus collisions at NLO

## TL;DR

This paper discusses the challenges and recent progress in achieving next-to-leading order accuracy in perturbative QCD calculations of particle production in proton-nucleus collisions, focusing on issues with negative cross-sections and running coupling schemes.

## Contribution

It reviews recent efforts to understand and resolve the negative cross-section problem in NLO calculations within the Color Glass Condensate framework and proposes a running coupling scheme for consistent process descriptions.

## Key findings

- Identification of the negative cross-section issue at NLO
- Development of a running coupling scheme for the formalism
- Progress towards reliable NLO predictions in high-energy QCD

## Abstract

Reaching next-to-leading order accuracy in perturbative calculations of particle production in QCD at high energy is essential for reliable phenomenological applications. In recent years, the Color Glass Condensate effective theory (the natural framework for such calculations) has indeed been promoted to NLO accuracy. However, the first NLO calculation of single-inclusive hadron production met with an unexpected difficulty: the cross-section suddenly turns negative at transverse momenta of the order of a few GeV, in a range where perturbation theory is expected to be reliable. We summarize recent efforts to understand and solve this issue, as well as to develop a running coupling scheme that can be used to consistently describe various processes in this formalism.