Differential cross sections for the exclusive reaction p →p→ppη observed via the η- π+π-π0 decay channel have been measured at Tbeam=2.15 GeV, 2.50 GeV, and 2.85 GeV (excess energies 324 MeV, 412 MeV, and 554 MeV). The influence of the N(1535)S11 resonance is clearly seen in the invariant mass and momentum dependent differential cross sections. The extracted resonance parameters are compatible with existing data. No significant evidence for further resonance contributions has been found. In addition, angular distributions of the pp η final state have been measured. The polar angle distribution of the η shows an anisotropy with respect to the beam axis for the lowest beam energy, which vanishes for the higher energies. The sign of this anisotropy is negative and expected to be sensitive to the dominant production mechanism. In contrast, the proton polar angle in the pp rest frame tends to be more strongly aligned along the beam axis with increasing beam energy. The analyzing power Ay is compatible with zero for all beam energies.
ASJC Scopus subject areas
- Nuclear and High Energy Physics