International Workshop
"The Structure and Dynamics of Hadrons"
Hirschegg, Kleinwalsertal, Austria -
Information

Title:	Mr.
Family Name:	Coderre
First Name:	Daniel
Gender:	male
E-Mail:	d.coderrefz-juelich.de
Affiliation for Badge:	FZJ, Jülich
Institute:	IKP
Address (Street):	Willhelm-Johnen Strasse
Postal Code, City:	52428 Jülich
Country:	Germany
Phone:	02461 61 3232
Fax:
Arrival Date:	January 16
Departure Date:	January 22
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Accommodation:	Waldemar-Petersen-Haus
Room Type:	Four-person room ( ~190 Euro )
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	As close as possible to conference site
Author(s):	Daniel Coderre for the WASA-at-COSY Collaboration
Institute(s):	Institut für Kernphysik and Jülich Center for Hadron Physics, Forschungszentrum Jülich, Germany, and Institut für Experimentalphysik, Ruhr Universität Bochum, Germany
Title of talk:	Measurement of the Rare Decay $\eta \rightarrow \pi^{+}\pi^{- }$e$^{+}$e$^{-}$ with WASA at COSY
Abstract:	The WASA-at-COSY physics program focuses on light meson decays using rare decays to investigate symmetries and symmetry breaking patterns. The analysis of the rare decay $\eta \rightarrow \pi^{+}\pi^{-}$e$^{+}$e$^{-}$ has two purposes: the measurement of the branching ratio and probing of a possible non standard model CP violation observable in the decay system. The existing experimental results on the branching ratio are not in agreement with modern theories, but the high rates of $\eta$ production at WASA-at-COSY will make a very precise measurement possible. It has also been postulated that the asymmetry between the electron and $\pi$ decay planes in the $\eta$ reference frame may be an observable for CP violation outside the standard model. Currently, the upper limit for this asymmetry is about 1\%. We have recorded about 3x10$^7$ $\eta$-mesons produced with the reaction $pd\rightarrow ^3$He$\eta$ and ~10$^8$ $\eta$-mesons produced with the reaction pp$\rightarrow$pp$\eta$ just above the kinematic threshold. The analysis focuses on correct identification of final state particles as well as efficient background rejection. A clean sample of signal event candidates has been identified in the proton-deuteron data allowing a preliminary determination of the total branching ratio. The decay has also been observed in higher- statistic proton-proton data though the analysis of this data is in its early stages. The presentation will focus on the current results as well as on the analysis techniques used to isolate the signal.
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