Novel Azimuthal Asymmetries in Drell Yan and Semi-inclusive Deep   Inelastic Scattering
  We consider the leading and sub-leading twist $T$-odd and even contributions to the $\cos 2\phi$ azimuthal asymmetry in unpolarized dilepton production in Drell-Yan Scattering. We estimate the contributions' effects at $500 {\rm GeV}$, $ 50 {\rm GeV}$, and $25 {\rm GeV}$ energies in the framework of the parton model using a quark diquark-spectator model of the nucleon to approximate the soft contributions. 
Leonard P. Gamberg, Gary R. Goldstein, and Karo A. Oganessyan