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Ultraperipheral collisions in hadron colliders give new opportunities to investigate the hadron structure through exclusive photoproduction processes. We describe the possibility of measuring the Generalized Parton Distributions in the Timelike Compton Scattering process and in the production of heavy vector meson. [ABSTRACT FROM AUTHOR]

Preliminary measurements are reported on the azimuthal single-spin asymmetries of exclusive ρ0 and π+ mesons for a transversely polarized hydrogen target at HERMES using the 27.6 GeV HERA lepton beam. Within the generalized parton distribution (GPD) formalism, hard exclusive vector meson production is sensitive to GPDs H and E, while pseudo-scalar meson production is sensitive to GPDs H and E. The extracted sin([lowercase_phi_synonym]-[lowercase_phi_synonym]s) azimuthal amplitude of the transverse target-spin asymmetry is compared to theoretical calculations based on GPD models. [ABSTRACT FROM AUTHOR]

The concept of Generalized Parton Distributions extends classical parton distributions by giving a “3-dimensional” view of the nucleons, allowing to study correlations between the parton longitudinal momentum and its transverse position in the nucleon. Measurements of such generalized distributions can be done with the COMPASS experiment, in particular using Deeply Virtual Compton Scattering events. They require to modify the set-up of COMPASS by introducing a recoil proton detector, an additional electromagnetic calorimeter and a new liquid hydrogen target. These upgrades are presently under study, and the first data taking could take place in 2010. © 2007 American Institute of Physics [ABSTRACT FROM AUTHOR]