Polarized and unpolarized $\mu$-pair meson-induced Drell--Yan production and the pion distribution amplitude

TL;DR

This paper analyzes muon pair production via pion-induced Drell-Yan processes, examining angular distributions to probe the pion distribution amplitude and comparing predictions with experimental data, including polarized targets.

Contribution

It provides a detailed QCD-based analysis of angular distributions in pion-induced Drell-Yan, testing different pion distribution amplitudes against experimental data and making predictions for polarized cases.

Findings

Angular distributions are sensitive to the pion distribution amplitude.

Predictions align with existing experimental data.

The study offers insights for the upcoming COMPASS experiment.

Abstract

We present a detailed analysis of meson-induced massive lepton (muon) Drell--Yan production for the process $\pi^{-}N\to\mu^{+}\mu^{-}X$, considering both an unpolarized nucleon target and longitudinally polarized protons. Using a QCD framework, we focus on the angular distribution of $\mu^+$, which is sensitive to the shape of the pion distribution amplitude, the goal being to test corresponding results against available experimental data. Predictions are made, employing various pion distribution amplitudes, for the azimuthal angle dependence of the $\mu^{+}$ distribution in the polarized case, relevant for the planned COMPASS experiment. QCD evolution is given particular attention in both considered cases.