Abstract

We show that measuring the cos 2 φ{symbol} 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 cos 2 φ{symbol} 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. © 2006.