Boer-Mulders function of pion meson and $q_T$-weighted $\cos 2\varphi$ asymmetry in the unpolarized ${\pi }^{-}p$ Drell-Yan at COMPASS

Abstract

We calculate the two leading-twist transverse momentum dependent distribution functions of the pion meson, the unpolarized distribution $f_{1\pi }(x,{\mathbf{k}}_T^2)$ and the Boer-Mulders function $h_{1\pi }^{\perp }(x,{\mathbf{k}}_T^2)$, using the pion wave functions derived from a light-cone approach. The evolution effect of the first ${\mathbf{k}}_T$-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 $\cos 2\varphi$ azimuthal asymmetry in the unpolarized ${\pi }^{-}p$ Drell-Yan process which can be measured at COMPASS in the near future.

Comments: 9 pages, 5 figures, match the version published in PRD