Single and double polarization observables in timelike Compton scattering off proton

We study the exclusive photoproduction of a lepton pair off the proton with the aim of studying the proton quark structure via the Generalized Parton Distributions (GPD) formalism. After deriving the amplitudes of the processes contributing to the $\gamma P\to P' e^+e^-$, the Timelike Compton Scattering and the Bethe-Heitler process, we calculate all unpolarized, single- and double- beam-target spin observables in the valence region in terms of GPDs.