The Structure of Absorptive Regge Cuts in theπpCharge-Exchange Reaction

Abstract

We analyze the ${\ensuremath{\pi}}^{\ensuremath{-}}p$ charge-exchange reaction above 5 GeV in a Regge-pole-plus-cut model. The absorption generating the cut is parametrized according to a geometrical picture in terms of a strength, radius, and diffuseness, and dispersion is introduced by a phase proportional to the absorption. The input Regge pole has no nonsense-wrong-signature zeros. We find the rescattering to be strongly energy-dependent and quite different in shape from elastic scattering near 6 GeV. However, as the energy increases to 18 GeV we find it approaching elastic scattering in shape and magnitude. The phase of the rescattering amplitude is crucial to understanding the structure of the polarization. At 6 GeV our scattering amplitudes, and, in particular, their pattern of zeros, agree with recent model-independent analyses, and differ from the results of most previous absorptive-model calculations. In the geometrical picture which emerges, the imaginary parts of the partial-wave amplitudes are peripheral, in accord with ideas proposed by Harari and others. Moreover, the real part of the helicity-flip amplitude is also peripheral, but the real part of the helicity-nonflip amplitude is not.