Twist expansion of Drell-Yan structure functions in color dipole approach

TL;DR

This paper investigates higher twist effects in the forward Drell-Yan process at the LHC using the color dipole model, deriving impact factors, performing twist expansion, and analyzing the breaking of the Lam-Tung relation.

Contribution

It introduces a twist expansion of Drell-Yan structure functions within the color dipole approach, including impact factor derivation and analysis of the Lam-Tung relation breaking at twist 4.

Findings

Twist expansion of Drell-Yan structure functions at arbitrary transverse momentum.

Explicit estimates of Lam-Tung relation breaking at twist 4.

Impact factors derived in Mellin representation for differential cross-sections.

Abstract

Forward Drell-Yan process at the LHC probes the proton structure at very small Bjorken-$x$ and moderate hard scales. In this kinematical domain higher twist effects may be significant and introduce sizeable corrections to the standard leading twist description. We study the forward Drell-Yan process beyond the leading twist approximation within the color dipole model framework that incorporates multiple scattering effects. We derive the Mellin representation of the forward Drell-Yan impact factors for fully differential cross-sections. These results combined with the color dipole cross-section of the saturation model are used to perform twist expansion of the Drell-Yan structure functions at arbitrary transverse momentum $q_T$ of the Drell-Yan pair and also of the structure functions integrated over $q_T$. We also investigate the Lam-Tung relation, find that it is broken at twist 4 and provide explicit estimates for the breaking term.