Novel hard exclusive QCD phenomena with hadron beams - measuring non-diagonal GPDs, high energy color transparency, etc.

• Mark Strikman (Pennsylvania State University (US))

We argue that CERN fixed target experiments with pion and proton beams and in particular NA61/SHINE can collect (already collected ?) the data which would allow to study a novel type of pQCD processes in which a high energy projectile splits into two hadrons with large p_t and comparable longitudinal momenta and a recoil nucleon (Delta -isobar) - for example \pi^- +n \to \pi^-\pi^- +p, \pi^-p--> \pi^-\pi^-+\Delta^{++},.... ( 2\to 3 processes). Use of the nuclear targets would allow to determine p_t range where color transparency regime sets in and perturbative QCD becomes applicable for description of large momentum transfer 2 \to 2 processes. In contrast to the previously proposed approaches for study of the dynamics of large angle elastic scattering, the discussed reactions allow to decouple the effects of the transverse size of configurations from effects of the space-time evolution of these configurations. As a result in these reaction three important QCD topics could be explored - 1) nucleon nondiagonal generalized parton distributions, 2) high - energy color transparency dynamics 3) pQCD predictions for the simplest large angle elastic scattering process \pi +(q\bar q) --> \pi + \pi.