Single spin asymmetry in $\pi p$ Drell-Yan process

Abstract

We study the single spin asymmetries for the $\pi p^{\uparrow }\to {\mu }^{+}{\mu }^{-}X$ process. We consider the asymmetries contributed by the coupling of the Boer-Mulders function with the transversity distribution and the pretzelosity distribution, characterized by the $\sin (\varphi +{\varphi }_S)$ and $\sin (3\varphi -{\varphi }_S)$ azimuthal angular dependence, respectively. We estimate the magnitude of these asymmetries at COMPASS by using proper weighting functions. We find that the $\sin (\varphi +{\varphi }_S)$ asymmetry is of the size of a few percent and can be measured through the experiment. The $\sin (3\varphi -{\varphi }_S)$ asymmetry is smaller than the $\sin (\varphi +{\varphi }_S)$ asymmetry. After a cut on $q_T$, we succeed in enhancing the asymmetry.

Comments: 11 pages, 2 figures, final version to appear in PLB