Helicity non-conservation in high energy exclusive scattering

A new mechanism for hadronic helicity flip in high energy hard exclusive reactions is studied. Its fundamental feature is the breaking of rotational symmetry of the hard collision by a scattering plane in processes involving independent quark scattering. An important role is played by 'chirally-odd' light-cone valence wave functions which carry non-zero orbital angular momentum and yet are leading in the high energy limit. There is no substantial suppression of the helicity violating process compared to helicity conserving ones as the momentum transfer Q2 is increased over the experimentally accessible region 1 GeV2 < Q2 < 100 GeV2. (author)