Elasticppandpp¯→ππ reactions in short- and middle-distance QCD

Arguments are presented for the expected behavior of the reaction pp¯→${\mathrm{\pi }}^{+}$ ${\mathrm{\pi }}^{\mathrm{-}}$ at high energy and large scattering angle. This reaction can have a sizable analyzing power, and both it and the scaled cross section ${\mathit{s}}^8$dσ/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 ${\mathit{A}}_{\mathit{n}\mathit{n}}$ can be explained simultaneously. As we will see, pp¯→${\mathrm{\pi }}^{+}$ ${\mathrm{\pi }}^{\mathrm{-}}$ 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 pp¯→${\mathrm{\pi }}^0$ ${\mathrm{\pi }}^0$ and ${\mathit{K}}^{+}$ ${\mathit{K}}^{\mathrm{-}}$) at a future SuperLEAR or KAON facility.