Single and double polarization asymmetries from deeply virtual $\pi^0$ production with a longitudinally polarized proton target

Deeply virtual exclusive meson production probes both the chiral-even generalized parton distributions (GPDs) and the chiral-odd transversity GPDs. The GPDs encode correlations of parton longitudinal momentum with transverse impact parameter as a function of the $x_B$ and $t$. The wide kinematic coverage of CLAS allowed measurements of exclusive $\pi^0$ electroproduction over the full azimuthal range. The resulting target and double-spin asymmetries were measured for the first time in the deep inelastic region. The experiment was carried out in Hall B at Jefferson Lab using a 6~GeV longitudinally polarized electron beam and a solid longitudinally polarized NH$_3$ target. All four final-state particles from the exclusive channel - electron, proton and two photons from $\pi^0$ decay - were identified. The azimuthal asymmetries in the hadronic center-of-mass system were fit, and their moments extracted. The data were compared to handbag-based calculations involving the contribution from both chiral-even and chiral-odd GPDs. The applicability of the formalism based on generalized parton distributions within the framework of the modified perturbative approach is discussed.