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

We show that measuring the cos2ϕ 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 h1⊥,d/h1⊥,u, which is still lack of theoretical constraint. The comparison of the cos2ϕ 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 h1⊥ effects or QCD vacuum effects are preferred by data.