On the cos2ϕ asymmetry in unpolarized leptoproduction

We investigate the origin of the cos2ϕ azimuthal asymmetry in unpolarized semi-inclusive DIS. The contributions to this asymmetry arising from the intrinsic transverse motion of quarks are explicitly evaluated, and predictions for the HERMES and COMPASS kinematic regimes are presented. We show that the effect of the leading-twist Boer-Mulders function h1⊥(x,kT2), which describes a correlation between the transverse momentum and the transverse spin of quarks, is quite significant and may also account for a part of the cos2ϕ asymmetry measured by ZEUS in the perturbative domain.