Detailed Analysis of Η Production in Proton-proton Collisions

Coupled-channel, multiresonance partial wave analysis (PWA), developed and used by Carnegie-Mellon-Berkeley analyses group (CMU-LBL 79) 1 has been recently very frequently used, and agreed as a potentially safe tool for extracting N * resonance parameters 2,3,4,5. The newly formed subsection for resonance parameter analyses of Baryon Resonance Analysis Group (BRAG) 6 has decided to re-evaluate relatively old analyses 1,7 , what has been suggested even by their own authors recently 8. BRAG has chosen three independent analyses which repeat the formalism suggested earlier, but with the use of new and improved data 9. They have come to a certain level of agreement regarding the number of poles and their values. However, some of the " Cutkosky " like analyses have been dropped out 10,11 , for technical reasons presumably. However, one possible direction of analysis has been dropped altogether. The question arises whether the obtained PWA can be " relatively " safely taken as input to processes involving more then two particles in the final state. Temporarily forgetting the expected additional complications (initial and final state interactions, off-mass shell behavior of two body amplitudes, etc.) this work tends to estimate whether the present two body T-matrices can account for the observables of a three body process pp → ppη, very carefully measured in Uppsala near the threshold 12. The special attention has been given to understanding the apparently inverted shape of the proton-eta differential cross section in the final state 12,13. The tendency of this work is not to improve the two body fit (which needs a lot of additional observables even to be semi-reliable,) but to see if the present T-matrices can explain the 2 → 3 body processes without drastic assumptions of the complications of the three body physics. The first, and natural test of the reliability of the two body amplitudes appeared in the carefully measured total and differential cross section for the process pp → ppη 12. We have developed a simple model based on the exchange of the lowest mesons depicted in the following figure: Unfortunately, there is a number of models which claim to reproduce the results, but differ among themselves drastically 14,16,15,17,18 , so it has been left to us to show that our model 19 , reduced to the assumptions of the mentioned models, gives a very similar result. The comparison is successfully made and will be shown elsewhere. The main idea …