Spin-density matrix elements in hard exclusive muoproduction of ω\omega mesons at COMPASS

Spin density matrix elements (SDMEs) have been determined forexclusive$\omega$ meson production on unpolarized protons, in the COMPASSkinematic region of 1.0 (GeV/c)$^2$ $= 2.1$~(GeV/c)$^2$), \left= 7.6~GeV/$c^2$and\left = 0.16~(GeV/c)$^2$) mean values.Using extracted SDMEs values the contribution of unnatural parity exchangeamplitudes andthe hypothesis of s-channel helicity conservation (SCHC) werestudied. Certain matrix elements e.g. $r^{5}_{00}$ corresponding totransition $\gamma^*_T \to V_L$ indicate violation of SCHC in exclusive $\omega$ production.A sizable contribution of unnatural parity exchange amplitudes is found for the exclusive $\omega$ meson muoproduction, and there is aclearindication of its decrease with increasing W

Beam-helicity asymmetries for single-hadron production in semi-inclusive deep-inelastic scattering from unpolarized hydrogen and deuterium targets

A measurement of beam-helicity asymmetries for single-hadron production in deep-inelastic scattering is presented. Data from the scattering of 27.6 GeV electrons and positrons off gaseous hydrogen and deuterium targets were collected by the HERMES experiment. The asymmetries are presented separately as a function of the Bjorken scaling variable, the hadron transverse momentum and the fractional energy for charged pions and kaons as well as for protons and anti-protons. These asymmetries are also presented as a function of the three aforementioned kinematic variables simultaneously