Initial-state energy loss in cold QCD matter and the Drell-Yan process

TL;DR

This paper investigates how initial-state energy loss in cold nuclear matter affects the Drell-Yan process, using a BDMPS-based model, and compares predictions with experimental data, revealing a violation of QCD factorization.

Contribution

It introduces a BDMPS-based energy loss model embedded in NLO calculations for Drell-Yan, providing new insights into nuclear effects and factorization violations.

Findings

Good agreement with E906 data despite magnitude differences

Energy loss effects are minimal at higher collision energies

First evidence of QCD factorization violation in pA Drell-Yan

Abstract

The effects of parton energy loss in nuclear matter on the Drell-Yan process in pA and $\pi$A collisions at fixed-target energies are investigated. Calculations are based on the Baier-Dokshitzer-Mueller-Peign\'{e}-Schiff (BDMPS) framework embedded in a next-to-leading order calculation, using the transport coefficient extracted from $J/\psi$ measurements. Model calculations prove in good agreement with preliminary measurements by the E906 experiment, despite a slightly different magnitude, supporting a consistent picture between Drell-Yan and $J/\psi$ data. Predictions for the COMPASS future measurements in $\pi$A collisions at $\sqrt{s}=18.9$~GeV are also performed. At higher collision energy ($\sqrt{s}=38.7$~GeV), Drell-Yan measurements are only slightly affected by energy loss effects. On the contrary, the E906 results turn out in clear disagreement with nuclear PDF effects alone. The comparison of E772, E866, and E906 measurements indicates for the first time a clear violation of QCD factorization in Drell-Yan production in pA collisions.