  Generalized parton distributions describe the correlations between the
longitudinal momentum and the transverse position of quarks and gluons in a
nucleon. They can be constrained by measuring photon leptoproduction
observables, arising from the interference between Bethe-Heitler and Deeply
virtual Compton scattering processes. At leading-twist/leading-order, the
amplitude of the latter is parameterized by complex integrals of the GPDs {H,
E, \~H, \~E} . As data collected on an unpolarized or longitudinally polarized
target constrains H and \~H, E is poorly known as it requires data collected
with a transversely polarized target, which is very challenging to implement in
fixed target experiments. The only alternative considered so far has been DVCS
on a neutron with a deuterium target, while assuming isospin symmetry and
absence of final-state interactions. Today, we introduce the polarization of
the recoil proton as a new DVCS observable, highly sensitive to E, which
appears feasible for an experimental study at a high-luminosity facility such
as Jefferson Lab.
