Recent Measurements of the cos(nφ[sub h]( Azimuthal Modulations of the Unpolarized Deep Inelastic Scattering Cross-section at HERMES

The cross section for hadron production in deep‐inelastic lepton scattering contains azimuthal modulations which can be related to transverse momentum dependent (TMD) distribution and fragmentation functions. The former provide a picture of how the quarks are moving within nucleons. Specifically, the cosφh and cos2φh modulations of the unpolarized cross section relate quark spin and quark transverse momentum. These moments have been carefully measured at the HERMES experiment in a fully differential way, as a function of x, y, z, and Ph⊥ for positive and negative hadrons produced from hydrogen and deuterium targets. These measurements give new access to the flavor dependent TMDs via their charge and target dependence. These data must be compared to comprehensive models to determine which terms contribute significantly to the cosφh and cos2φh moments and allow access to the underlying structure functions.