Cold nuclear matter effects on azimuthal decorrelation in heavy-ion collisions

TL;DR

This paper investigates the validity of factorization in heavy-ion collisions by calculating cold nuclear matter effects on azimuthal decorrelation in Drell-Yan and boson-jet processes, using Glauber modeling.

Contribution

It introduces a setup to study hard processes and bulk nuclear matter simultaneously, and calculates leading-order cold nuclear matter corrections without radiation effects.

Findings

Factorization holds at leading order for both processes.

Cross sections factorize into hard parts and medium-modified distributions.

Cold nuclear matter effects can be incorporated via convolution with medium-modified functions.

Abstract

The assumption of factorization lies at the core of calculations of medium effects on observables computable in perturbative Quantum Chromodynamics. In this work we examine this assumption, for which we propose a setup to study hard processes and bulk nuclear matter in heavy-ion collisions on the same footing using the Glauber modelling of heavy nuclei. To exemplify this approach, we calculate the leading-order corrections to azimuthal decorrelation in Drell-Yan and boson-jet processes due to cold nuclear matter effects, not considering radiation. At leading order in both the hard momentum scale and the nuclear size, the impact-parameter dependent cross section is found to factorize for both processes. The factorization formula involves a convolution of the hard cross section with the medium-modified parton distributions, and, for boson-jet production, the medium-modified jet function.