Reinvestigation of $pp\to ppπ^0$ and $pp\to ppη$ at threshold

Abstract

$pp\to ppπ^0$ and $pp\to ppη$ were considered close to threshold. The pion production was found not only to be dominated by impulse approximation (IA) and rescattering contributions, but also strongly by box-diagrams, resonances and heavy-meson exchanges. New relevant contributions for the IA were found. The role of the offshell behaviour of nucleon-resonance couplings ($P_{11}(1440), S_{11}(1535)$) and of interference effects for the eta production was investigated. The results opened a large door for microsopic understanding of short range physics. A covariant model for $pp\to ppη$ being under construction is going to be finished.