Angular Distributions in unpolarized proton-induced Drell-Yan process

We will report a measurement of the angular distributions of Drell-Yan dimuons produced using an 800 GeV/c proton beam on a deuterium target. The muon angular distributions in polar angle $\theta$ and azimuthal angle $\phi$ have been measured over the kinematic range $4.5 < m_{\mu \mu} < 15$ GeV/c$^2$, $0 < p_T < 4 $ GeV/c, and $0 < x_F < 0.8$. The data will be compared with the angular distribution in unpolarized pion-induced Drell-Yan, in terms of angular coefficients and the Lam-Tung relation. The expectations from two models will be discussed. One involves QCD vacuum effect and the other involves transverse-momentum-dependent Boer-Mulders structure function $h_1^\perp$. The preliminary results with proton target will be also presented.