Exclusive hadronic reactions at high Q2 (90 degrees) and polarization phenomena, an experimental proposal

Arguments are presented for the expected behaviour of πN → πN scattering and the bar pp → π-π+ reaction at high energy and large scattering angles. The annihilation reaction has close to maximal asymmetry (∼ 1) for plab≤ 2.2 GeV/c. As will be presented for fixed (90 degrees) angle this large asymmetry will not become zero but will start to oscillate with energy at higher energies and large Q2 when perturbative QCD becomes applicable. This is due to the energy dependence of a phase difference between the independent quark-quark scattering (Landshoff) and short-distance processes at high but not asymptotic energies. A consequence of the existence of the Landshoff process is that even if helicity is conserved at the quark level (mq = 0 MeV), helicity does not have to be conserved on the hadronic level. The authors will discuss the implications for spin observables in pp elastic scattering and argue that these QCD phenomena are easier to explore theoretically in the πN → πN scattering and/or in the crossed channel reaction bar pp → π-π+ where the analysis is simpler because these two processes have only two helicity amplitudes