文摘
Exclusive production of mesons was studied at the COMPASS experiment by scattering muons off transversely polarised protons. Five single-spin and three double-spin azimuthal asymmetries were measured as a function of , , or . The asymmetry is found to be . All other asymmetries are also found to be of small magnitude and consistent with zero within experimental uncertainties. Very recent calculations using a GPD-based model agree well with the present results. The data is interpreted as evidence for the existence of chiral-odd, transverse generalized parton distributions.