Investigations of azimuthal asymmetry in semi-inclusive leptoproduction

Abstract. We consider the azimuthal asymmetries in semi-inclusive deep inelastic leptoproduction arising due to both perturbative and nonperturbative effects at HERMES energies and show that the $k_T^2/Q^2$ order corrections to $\langle \cos\phi \rangle$ and $\langle \cos2\phi \rangle$ are significant. We also reconsider the results of perturbative effects for $\langle \cos\phi \rangle$ at large momentum transfers [1] using the more recent sets of scale-dependent distribution and fragmentation functions, which bring up to 18% difference in $\langle \cos\phi \rangle$. In the same approach we calculate the $\langle \cos2\phi \rangle$ as well.