ELASTIC PP AND P(P)OVER-BAR-]PI-PI REACTIONS IN SHORT-DISTANCE AND MIDDLE-DISTANCE QCD

Arguments are presented for the expected behavior of the reaction ppBAR --> pi+pi- at high energy and large scattering angle. This reaction can have a sizable analyzing power, and both it and the scaled cross section s8dsigma/dt will oscillate with energy since the QCD phase difference between the independent scattering (Landshoff) and short-distance processes is energy dependent at high but not superasymptotic energies. The argument follows studies of pp elastic scattering, where we update the fits to its scaled cross section and show that the behavior of the double polarization quantity A(nn) can be explained simultaneously. As we will see, ppBAR --> pi+pi- is theoretically simpler than pp elastic scattering because it has only two helicity amplitudes. Furthermore, it would be possible to measure this reaction (and also ppBAR --> pi0pi0 and K+K-) at a future SuperLEAR or KAON facility.