Photon-exchange processes at hadron colliders as a probe of the dynamics   of diffraction
  The rich structure of photon-exchange processes at hadron colliders is studied. We discuss central vector meson production pp --> p + J/psi + p, W production pp --> p + W + X and mu+ mu- production. Each process has distinct, and large, soft pp rescattering effects, which can be directly observed by detecting the outgoing protons. This allows a probe of the optical density of the proton, which plays a crucial role in the evaluation of the rapidity gap survival probabilities in diffractive-like processes at hadron colliders. We note that an alternative mechanism for J/psi production is odderon, instead of photon, exchange; and that the ratio of odderon to photon contributions is enhanced (suppressed) for phi(Upsilon) vector meson production. 
V.A. Khoze (Durham), A.D. Martin (Durham), and M.G. Ryskin (St.   Petersburg)