Azimuthal asymmetry in unpolarized $\pi N$ Drell-Yan process

Abstract

Taking into account the effect of final state interaction, we calculate the non-zero (naïve) $T$-odd transverse momentum dependent distribution $h_1^{\perp }(x,{\text{kp}}^2)$ of the pion in a quark-spectator-antiquark model with effective pion-quark-antiquark coupling as a dipole form factor. Using the model result we estimate the $\cos 2\varphi$ asymmetries in the unpolarized ${\pi }^{-}N$ Drell-Yan process which can be expressed as $h_1^{\perp }\times {\bar{h}}_1^{\perp }$. We find that the resulting $h_{1\pi }^{\text{p}}(x,{\text{kp}}^2)$ has the advantage to reproduce the asymmetry that agrees with the experimental data measured by NA10 Collaboration. We estimate the $\cos 2\varphi$ asymmetries averaged over the kinematics of NA10 experiments for 140, 194 and 286 GeV ${\pi }^{-}$ beam and compare them with relevant experimental data.

Comments: 11 pages, 4 figures, to appear in PLB