Exclusive photoproduction of lepton pairs at LHC

Exclusive photoproduction of dileptons, γp→ℓ+ℓ−p, will be measured in ultraperipheral collisions at LHC. The mechanism where the lepton pair comes from a heavy timelike photon radiated from a quark interferes with the pure QED process γγ→ℓ+ℓ−. As an analog of deeply virtual Compton scattering, this timelike Compton scattering is a way to study generalized parton distributions in the nucleon or the nucleus. High energy kinematics will enable to focus on gluon distributions. Nuclear effects may be scrutinized in heavy-ion collisions.