Single spin asymmetry in πp Drell-Yan process

We study the single spin asymmetries for the πp↑→μ+μ−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(ϕ+ϕS) and sin(3ϕ−ϕS) azimuthal angular dependence, respectively. We estimate the magnitude of these asymmetries at COMPASS by using proper weighting functions. We find that the sin(ϕ+ϕS) asymmetry is of the size of a few percent and can be measured through the experiment. The sin(3ϕ−ϕS) asymmetry is smaller than the sin(ϕ+ϕS) asymmetry. After a cut on qT, we succeed in enhancing the asymmetry.