# Lepton angular distributions of Drell-Yan process in pQCD and a geometric approach

## TL;DR

This paper investigates lepton angular distributions in the Drell-Yan process using perturbative QCD at NLO and NNLO, and introduces a geometric approach to understand key features of the distributions and Lam-Tung relation violations.

## Contribution

It provides detailed calculations of angular parameters in Drell-Yan processes and offers a geometric interpretation of their dependence on kinematic variables.

## Key findings

- Calculated angular parameters for E615 and predictions for COMPASS.
- Qualitative understanding of transverse momentum and rapidity dependence.
- Insights into violation of the Lam-Tung relation.

## Abstract

The lepton angular distributions of the Drell-Yan process in the fixed-target experiments are investigated by NLO and NNLO perturbative QCD. We present the calculated angular parameters $\lambda$, $\mu$, $\nu$ and the degree of violation of the Lam-Tung relation, $1-\lambda-2\nu$, for the E615 experiment as well as predictions for the COMPASS experiment. Many salient features of transverse momentum and rapidity dependence could be qualitatively understood by a geometric approach.