The Cos 2? Asymmetry In The Unpolarized Drell-yan Of ?~-p

In quantum chromodynamics(QCD)spin physics,investigating the spin-related asym-metries in hard scattering processes is an important approach to understand the nontrivial quark and spin structure of hadrons.The cos 2? angular asymmetry observed in unpolarized Drell-Yan processes has been measured by several experiments.Particularly,in pion-induced Drell-Yan?-N??+?-X,the data show large values of angular asymmetry factor ?.The result can not be explained by the leading-twist collinear factorization in QCD.Boer proposed that the con-volution of two Boer-Mulders functions,each coming from one of the two incident hadrons,can provide leading-twist contribution to the cos 2? angular asymmetry.The Boer-Mulders function is a transverse momentum dependent(TMD)distribution function which describes the transversely polarization distribution of the quark inside an unpolarized hadron.In recent years,the model calculation of the Boer-Mulders function has also been extended to the case of the pion meson.To study the correlation between the Boer-Mulders function and the cos 2? angular asymmetry,unpolarized ?-N Drell-Yan process is an appropriate approach.In our work,we calculate the unpolarized distribution function and the Boer-Mulders function of the pion meson using the pion wave functions derived from the light-cone approach.In the calculation of the pion Boer-Mulders function,we use the overlap integration of the light-cone wave functions.The evolution effect of Boer-Mulders function is also considered.We present our prediction on the transverse momentum weighted cos 20 asymmetry in the unpolarized ?-p Drell-Yan process at the kinematics of COMPASS experimence group.