Gießen 2007 – scientific programme
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HK: Fachverband Physik der Hadronen und Kerne
HK 35: Elektromagnetische und Hadronische Sonden
HK 35.4: Talk
Wednesday, March 14, 2007, 17:45–18:00, A
Mechanism of near-threshold production of the η meson by means of the analysing power measurements — •Rafal Czyzykiewicz1,2 and Pawel Moskal1,2 for the COSY-11 collaboration — 1Institute of Physics, Jagellonian University, 30-059 Cracow, Poland — 2IKP, Forschungszentrum Jülich, 52425 Jülich, Germany
We report on measurements of the analysing power Ay for the p→p→ ppη reaction. Experiments have been performed in the near threshold energy regime at beam momenta of pbeam=2.010 and 2.085 GeV/c, corresponding to excess energies of Q = 10 and 36 MeV, respectively. The experiments were realised by means of the cooler synchrotron and storage ring COSY along with a cluster jet target. For registration of the reaction products the COSY-11 facility was used. The identification of the η meson has been performed with the missing mass method.
Results for the angular dependence of the analysing power combined with the previously determined isospin dependence of the total cross section for the η meson production in nucleon-nucleon collisions reveal statistically significant evidence that the excitation of the nucleon to the S11 resonance, the process which intermediates the production of the η meson, is predominantly due to the exchange of a π meson between the colliding nucleons.
The determined values of the analysing power are consistent with zero implying that the η meson is produced predominantly in the s-wave at both studied excess energies.