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HK: Fachverband Physik der Hadronen und Kerne
HK 24: Hadronenstruktur und -spektroskopie VI
HK 24.2: Talk
Tuesday, March 22, 2011, 17:00–17:15, C-2
Precision measurement of the η-meson mass at ANKE-COSY — •Paul Goslawski, Ingo Burmeister, Malte Mielke, Michael Papenbrock, Alexander Täschner, and Alfons Khoukaz — Institut für Kernphysik, Universität Münster, D-48149 Münster, Germany
Measurements of the mass of the η-meson performed at different experimental facilities (i.e. COSY-GEM, MAMI, CLEO, KLOE, NA48) over the last decade have resulted in very precise data which differ by up to 0.5 MeV/c2, i.e., more than eight standard deviations. In order to clarify this situation a new measurement of the dp→3He η reaction near threshold was proposed at the COoler SYnchrotron - COSY - of the Forschungszentrum Jülich with the aim to achieve a mass resolution of Δ m < 50 keV/c2.
In order to measure the η meson mass with high accuracy through the dp→ 3He η reaction, the momentum of the circulating deuteron beam in COSY has to be determined with unprecedented precision. This has been achieved by studying the spin dynamics of the polarised deuteron beam. By depolarising the beam through the use of an artificially induced spin resonance, it was possible to determine the beam momentum p with an accuracy of Δ p/p < 10−4 for p≈ 3 GeV/c. In parallel the CMS momenta of the produced 3He nuclei have to be determined with high precision with the ANKE spectrometer. The method for determination of the η mass, as well as current results will be discussed in this presentation.
Supported by the COSY-FFE program.