Higher partial waves in pp→ppη near threshold

Abstract

Exclusive measurements of the production of η-mesons in the pp → ppη reaction have been carried out at excess energies of 16 and 37 MeV above threshold. The deviations from phase space are dominated by the proton-proton final state interaction and this influences particularly the energy distribution of the η meson. However, evidence is also presented at the higher energy for the existence of an anisotropy in the angular distributions of the η-meson and also of the final proton-proton pair, probably to be associated with D-waves in this system interfering with the dominant S-wave term. The sign of the η angular anisotropy suggests that ρ-exchange is important for this reaction.

Production of η and η′ mesons on nucleons and nuclei

“…More detailed information can be obtained from looking at differential distributions of the pp → ppη reaction in data taken at a single energy [212,213]. The spectrum of the excitation energy E pp in the pp system is shown in Fig.…”

Detailed Analysis of Η Production in Proton-Proton Collisions

“…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 .…”

“…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 semireliable, ) 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:…”

“…The comparison is successfully made and will be shown elsewhere. The main idea of this presentation is to draw atten- tion to the fact that the differential pη cross sections in a three body process tends to show a different curvature when compared to the two body π − p → ηn process which should dominate the process 12 . In spite of the additional uncertainties of the processes like ISI, FSI and off-mass shell extrapolation of two body amplitudes, the effects should be extremely high, and acting in the same direction in order to turn the slope of the differential cross section.…”