On γ N to γ rho N' at large γ rho invariant mass

Photoproduction of a pair of particles with large invariant mass is a natural extension of collinear QCD factorization theorems which have been much studied for deeply virtual Compton scattering and deeply virtual meson production. We consider the case where the wide angle Compton scattering subprocess $\gamma (q\bar q) \to \gamma \rho $ factorizes from generalized parton distribution. At dominant twist, separating the transverse (respectively longitudinal) polarization of the $\rho$ meson allows one to get access to chiral-odd (respectively chiral-even) GPDs. This opens a new way to the extraction of these elusive transversity GPDs.