Spin dependence of η meson production in proton-proton collisions close to threshold

Abstract

Taking advantage of the high acceptance and axial symmetry of the WASA-at-COSY detector, and the high degree of the polarized proton beam of COSY, the reaction pp{\to} ppη has been measured close to threshold to explore the analyzing power Ay. The angular distribution of Ay is determined with the precision improved by more than one order of magnitude with respect to previous results allowing a first accurate comparison with theoretical predictions. The determined analyzing power is consistent with zero for an excess energy of Q = 15 MeV signaling s wave production with no evidence for higher partial waves. At Q = 72 MeV the data reveals strong interference of P s and P p partial waves and cancellation of (P p) and Ss*Sd contributions. These results rule out the presently available theoretical predictions for the production mechanism of the η meson.

Accepted for publication in Phys. Rev. Lett

References in corpus (5)

• The WASA Detector Facility at CELSIUS
• Production of $\eta$ and ${\eta }^{\prime }$ Mesons on Nucleons and Nuclei
• Mechanism of the close-to-threshold production of the eta meson
• Near threshold production of the eta meson via the quasi-free pn --> pn eta reaction
• Eta meson production in nucleon-nucleon collisions within an effective Lagrangian model