Overlap function analysis of πWENA elastic and charge exchange scattering at high energies

Abstract

In terms of overlap functions, a new kind of analysis of πOpen image in new window elastic and charge exchange scattering data at high energies and small momentum transfers is given. The data analysed cover a range 6 GeV/c≾qL=pion laboratory momentum ≾18 GeV/c and 0≤−t=(centre-of-mass momentum transfer)2 ≾1 (GeV/c)2. The phenomenological expressions of the scattering amplitudes, including spin-flip, as they are obtained from experiment, are traced back to simple forms for the π±p overlap functions. The latter are interpreted in terms of different classes of inelastic π±p collisions, each contributing with a characteristic power ofs=(centre-of-mass energy)2 to the overlap functions. The dominant deviations from the genuine asymptotic situation (where π+p and π-p elastic scattering are expected to be identical) are attributed to the presence of «charge annihilation channels» among π-p inelastic transitions which have no counterpart among the π+p inelastic transitions. In this context the concepts of absorptive corrections and of a common interaction volume for both elastic and inelastic collisions are encountered within the overlap function framework. The actual simple forms we have adopted for the overlap functions imply that the charge exchange peak must remain somewhat broader than the elastic ones, so that in the case of constancy of the latter the observed shrinkage of the former is predicted to slow down and stop, or alternatively but less plausibly, elastic peaks have to start to shrink, the change occurring at an energy somewhat higher than the ones here studied and which is estimated to beqL≅26 GeV/c. Another implication of our overlap functions is that the Reggeized ρ-exchange form of the charge exchange amplitude is supplemented by small corrections. As will be shown in a succeeding paper, these account in a natural manner for the measured polarization in π-p → π0n. Also the π±p → π±p polarizations will be shown to be satisfactorily described in the present formalism.