Protoninduced Pion-, Eta- and Kaon-Production at Threshold

Abstract

We present some details of our recent theoretical investigations on the total cross section of the reactions $pp\to pp π^0$, $pp\to pp η$ and $pp\to pΛK^+$ at threshold. Applying standard nonrelativistic perturbation theory within the framework of meson exchange models (MEC) to all of the investigated processes we observe that theory is still far--off from a quantitative understanding of the existing data, although the qualitative behaviour of the threshold cross sections can be reproduced. The often quoted $η^2$--dependence of the $pp\to pp π^0$ cross section at threshold is due to a calculational mistake of Koltun and Reitan (1966) and not based on theoretical grounds, where threebody phasespace behaviour would yield $η^4$, which can be affected by final state and short range effects. To respect the high momentum transfers for $pp\to pp η$ and $pp\to pΛK^+$ relativistic models were developed. Hereby the $η$--production still is based on MEC, while the $K^+$ production was investigated in the quark-gluon-picture based on the Bethe--Salpeter formalism.