Threshold Perspectives on Meson Production

Studies of meson production in nucleon–nucleon collisions at threshold are characterised by few degrees of freedom in a configuration of well defined initial and final states with a transition governed by short range dynamics. Effects from low–energy scattering in the exit channel are inherent to the data and probe the interaction in baryon–meson and meson–meson systems otherwise difficult to access. From dedicated experiments at the present generation of cooler rings precise data are becoming available on differential and eventually spin observables allowing detailed comparisons between complementary final states. To discuss physics implications of generic and specific properties, recent experimental results on meson production in proton–proton scattering obtained at CELSIUS and COSY serve as a guideline.