Threshold meson production in nucleon-nucleon collisions

Abstract

A brief overview on recent model calculations for near threshold pion production in nucleon-nucleon collisions is given. Results from our own investigations of the reactions $pp\to pp\ddot{I}{€}^0$ and $pn\to d\ddot{I}{€}^0$ are presented. Direct production, heavy meson exchange and pion rescattering are taken into account. For the latter a T-matrix obtained from a microscopic model of the $\ddot{I}€N$ interaction is employed. We obtain a significant contribution from rescattering, but not enough to describe the data for $pp\to pp\ddot{I}{€}^0$. The missing production rate can be provided by heavy meson exchanges. For the first time the effect of off--shell rescattering is investigated for the reaction $pn\to d\ddot{I}{€}^0$. Isoscalar rescattering in combination with isovector rescattering is able to describe the s-wave production data. We confirm that heavy meson exchanges are negligible in this reaction.

15 pages, 10 figures, contribution to the workshop MESON96, Cracow, Poland, 10-14 May 1996