Bochum 2009 – scientific programme
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HK: Fachverband Hadronen und Kerne
HK 56: Hadron Structure and Spectroscopy I
HK 56.6: Talk
Wednesday, March 18, 2009, 18:00–18:15, H-ZO 20
Precision Measurement of the η-Mass at COSY-ANKE — •Paul Goslawski, Alfons Khoukaz, Malte Mielke, Michael Papenbrock, Tobias Rausmann, and Alexander Täschner — Institut für Kernphysik, Westfälische-Wilhelms-Universität Münster, Münster, Germany
Recent measurements on the η meson mass performed at different experimental facilities (i.e. COSY-GEM, MAMI, CLEO, KLOE, NA48) resulted in very precise data but differ partly by up to more than eight standard deviations, i.e. 0,5 MeV/c2. In order to clarify this situation a new high precision measurement using the ANKE spectrometer at the COoler SYnchrotron - COSY - has been realised in March 2008. Using the two-body reaction dp → 3Heη at low excess energies the η mass can be determined only from pure kinematics by the determination of the production threshold. To obtain a total uncertainty of Δ mη < 50 keV/c2 on the η mass the beam momentum has to be determined with an accuracy of Δ p / p = 5 · 10−5. This can be achieved by using an artificial spin resonance which can be induced by a horizontal rf magnetic field from a solenoid. With such a spin resonance a vector polarized deuteron beam can be depolarized depending on the revolution frequency and the beam momentum.
The method for determination of the η mass as well as preliminary results for the high precision beam momentum evaluation will be shown in this presentation.
Supported by the COSY-FFE program.