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Berlin 2005 – scientific programme

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HK: Physik der Hadronen und Kerne

HK 22: Postersitzung

HK 22.7: Poster

Monday, March 7, 2005, 16:30–18:00, TU MA141

Analysing power measurements for the ppppη reaction at COSY-11 — •Rafał Czyżykiewicz — IKP, FZ-Jülich, Germany — Jagellonian University, Kraków, Poland

Supported by FZ-Jülich and DAAD.
It is generally expected that in NN collisions the η meson is predominantly created via the mesonic excitation of the S11(1535) resonance, and its subsequent decay into a proton-η system. At present it is still not established what the relative production amplitudes for the S11(1535) resonance are. Among the available models Nakayama et al. [1] postulated a dominance of π and η as exchange mesons, while Fäldt and Wilkin [2] found a main contribution originating from the vector meson exchange. Both models are in good agreement with unpolarised observables, however they differ significantly when predicting polarisation observables – such as the analysing power Ay.

In this contribution we report on the COSY-11 measurements of Ay for the ppppη reaction [3] determined at different close-to-threshold energies. The techniques of the polarisation determination at COSY-11 and their comparison with the results [4,5] obtained by means of the other polarimeters operating at COSY will be presented.
[1] K. Nakayama et al., Phys. Rev. C 65 (2002) 045210.
[2] G. Fäldt and C. Wilkin, Phys. Scripta  64 (2001) 427.
[3] COSY-11: P. Winter et al., Phys. Lett. B 544 (2002) 251; erratum-ibid. B 553 (2003) 339.
[4] B. Lorentz, FZ-Jülich, private communication (2003).
[5] K. Ulbrich, Bonn University, private communication (2003).

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