F. Giordano

Measurement of azimuthal asymmetries of the unpolarized cross section at HERMES

A multi‐dimensional (x, y, z, Ph⊥) extraction of cosu2009φh and cosu20092φh azimuthal asymmetries of unpolarized Semi‐Inclusive Deep Inelastic Scattering at HERMES is discussed. The use of data taken with hydrogen and deuterium targets and the separation of positive and negative hadrons allow to access flavor‐dependent information about quark intrinsic transverse momenta and spin‐orbit correlations. This flavor sensitivity allows for a discrimination between theoretical models in the HERMES kinematic regime.

Flavor-dependent azimuthal modulations in unpolarized SIDIS cross section at HERMES

The cos h and cos 2h azimuthal modulations of the unpolarized hadron Semi-Inclusive Deep Inelastic Scattering cross section are sensitive to the quark intrinsic transverse momentum and transverse spin. These modulations have been measured at HERMES in a fully differential way by means of a 4-dimensional unfolding procedure to correct for instrumental effects. Results have been extracted for hydrogen and deuterium targets and separately for positively and negatively charged pions and kaons, to access flavor-dependent information about the nucleon internal transverse degrees of freedom.

Fragmentation function measurements at Belle

The precision measurement of fragmentation functions is an important requirement to study the spin structure of the nucleon. Unpolarized fragmentation functions at reasonably low scale and high fractional energy are necessary to complement the measurements mostly performed at LEP in order to obtain high enough precision for measurements at semi‐inclusive DIS experiments and at RHIC. Those can be obtained from the abundant data collected with the Belle detector at the e+e− collider KEKB. In addition one can cleanly measure the transversely polarized fragmentation functions such as the Collins fragmentation function and the interference fragmentation functions. Both have been obtained with great precision at Belle.

Recent Measurements of the cos(nφh( 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.