# Boer-Mulders function of pion meson and $q_T$-weighted $\cos2\phi$ asymmetry in the unpolarized $\pi^- p$ Drell-Yan at COMPASS

## TL;DR

This paper computes the pion's transverse momentum dependent distributions, including the Boer-Mulders function, and predicts the $m{k}_T$-weighted $ ext{cos}2 ext{phi}$ asymmetry in unpolarized $ ext{pi}^- ext{p}$ Drell-Yan processes for future experimental verification at COMPASS.

## Contribution

It introduces a light-cone approach to calculate the pion's TMDs and models the evolution of the Boer-Mulders function to predict measurable asymmetries in Drell-Yan processes.

## Key findings

- Calculated the pion's unpolarized and Boer-Mulders TMDs using light-cone wave functions.
- Studied the evolution effect of the Boer-Mulders function's first $m{k}_T$-moment.
- Predicted the $ ext{cos}2 ext{phi}$ asymmetry in $ ext{pi}^- ext{p}$ Drell-Yan at COMPASS.

## Abstract

We calculate the two leading-twist transverse momentum dependent distribution functions of the pion meson, the unpolarized distribution $f_{1\pi}(x,\bm{k}^2_T)$ and the Boer-Mulders function $h_{1\pi}^\perp (x,\bm{k}^2_T)$, using the pion wave functions derived from a light-cone approach. The evolution effect of the first $\bm k_T$-moment of the pion Boer-Mulders function is studied by employing an approximate evolution kernel. Using the model resulting distributions, we predict the transverse momentum weighted $\cos2\phi$ azimuthal asymmetry in the unpolarized $\pi^- p$ Drell-Yan process which can be measured at COMPASS in the near future.