Nuclear dependence of azimuthal asymmetry in semi-inclusive deep inelastic scattering

Within the framework of a generalized factorization, semi-inclusive deeply inelastic scattering (SIDIS) cross sections can be expressed as a series of products of collinear hard parts and transverse-momentum-dependent (TMD) parton distributions and correlations. The azimuthal asymmetry < cos phi > of unpolarized SIDIS in the small transverse-momentum region will depend on both twist-2 and -3 TMD quark distributions in target nucleons or nuclei. Nuclear broadening of these twist-2 and -3 quark distributions due to final-state multiple scattering in nuclei is investigated and the nuclear dependence of the azimuthal asymmetry < cos phi > is studied. It is shown that the azimuthal asymmetry is suppressed by multiple parton scattering and the transverse-momentum dependence of the suppression depends on the relative shape of the twist-2 and -3 quark distributions in the nucleon. A Gaussian ansatz for TMD twist-2 and -3 quark distributions in nucleon is used to demonstrate the nuclear dependence of the azimuthal asymmetry and to estimate the smearing effect due to fragmentation.