Comparison of regge models of pion-nucleon scattering and related processes

Abstract

A phenomenological analysis of pion nucleon scattering at high energies is presented in terms of soveral absorptive models for the πN amplitudes. In the past there have been two popular versions - the weak-cut model and the strong-cut model. In general it was difficult to choose between these- two very different approaches. However the whole absorptive approach was thrown into doubt when better information about the polarization in π p→ π(^o) n at larger ׀t׀ became available, last year. The new data in fact accords with the predictions of the p + p(^1) polo lit of Barger and Phillips, More recently measurements of the R parameter in π(^+)ρ→ π(^+)ρ have enabled the phases of the πN amplitudes to be determined, and again these agree with the Barber-Phillips (B.P) productions but contradict both types of absorption model. We assume that the B.P It = 0 amplitudes are a reliable T-representation of these amplitudes, and we fit those with a somewhat simpler parameterization. For our I(_t). = 1 amplitudes, we find that a t-channel parameterization plus crossing was much preferred to the usual direct s-channel parameterization. We find, cy correctly taking into account the real parts of the I(_t) = 0 non-flip amplitude i.e essentially, by including a p o p cut contribution in the I(_t) = 1 amplitudes, that our fits improved considerably, especially the charge-exchange polarization. We find that the fixed-pole coupling model is by far the best. In general the data is reasonably well fitted apart from the high ׀t| region of our elastic polarisation. This is traced back to our rather poor representation of the real parts of the I(_t) = 1 amplitudes. It is unlikely that a better representation of the- I(_t) = 0 amplitudes will remedy this defect. The imaginar parts of these amplitudes- are in good agreement with amplitude analysis. We conclude that the absorption prescription, with any hypothesis about the choosing mechanism of the p pole is not completely successful in explaining the I(_t)= 1 amplitudes. It works well for the imaginary parts and less so for the real parts, and we indicate, possible, reasons for this.