Flavor separation of the Boer-Mulders function from unpolarized $π^- p$ and $π^- D$ Drell-Yan processes

Abstract

We show that measuring the $\cos 2ϕ$ angular dependence in unpolarized Drell-Yan processes with $π^-$ beams colliding on proton and deuteron targets can determine the ratio of the Boer-Mulders functions for $d$ and $u$ quarks inside the proton $h_1^{\perp,d}/h_1^{\perp,u}$, which is still lack of theoretical constraint. The comparison of the $\cos 2 ϕ$ asymmetries measured in unpolarized $π^- p$ and $π^- D$ Drell-Yan processes, which are accessible at CERN by the COMPASS collaboration, can help to discriminate whether $h_1^\perp$ effects or QCD vacuum effects are preferred by data.