1207.3710 (A. Nikolaev et al.)

Determination of the η mass with the Crystal Ball at MAMI-B    [PDF]

A. Nikolaev, P. Aguar-Bartolomé, J. Ahrens, J. R. M. Annand, H. J. Arends, R. Beck, V. Bekrenev, B. Boillat, A. Braghieri, D. Branford, W. J. Briscoe, J. W. Brudvik, S. Cherepnya, R. Codling, M. Dehn, E. J. Downie, L. V. Fil'kov, D. I. Glazier, R. Gregor, E. Heid, D. Hornidge, O. Jahn, A. Jankowiak, K. -H. Kaiser, V. L. Kashevarov, R. Kondratiev, M. Korolija, M. Kotulla, D. Krambrich, B. Krusche, M. Lang, V. Lisin, K. Livingston, U. Ludwig-Mertin, S. Lugert, I. J. D. MacGregor, D. M. Manley, M. Martinez-Fabregate, J. C. McGeorge, D. Mekterovic, V. Metag, B. M. K. Nefkens, R. Novotny, R. O. Owens, P. Pedroni, A. Polonski, S. N. Prakhov, J. W. Price, A. Reiter, G. Rosner, M. Rost, T. Rostomyan, S. Schumann, D. Sober, A. Starostin, I. Supek, C. M. Tarbert, A. Thomas, M. Unverzagt, Th. Walcher, D. P. Watts, F. Zehr

A new precise determination of the {\eta} meson mass is presented. It is based on a measurement of the threshold for the {\gamma}p -> p{\eta} reaction using the tagger focal-plane microscope detector at the MAMI-B facility in Mainz. The tagger microscope has a higher energy resolution than the standard tagging spectrometer and, hence, allowed an improvement in the accuracy compared to the previous {\eta} mass measurement at MAMI-B. The result m{\eta} = (547.851 +- 0.031 stat. +- 0.062 syst.) MeV agrees very well with the precise values of the NA48, KLOE and CLEO collaborations and deviates by about 5{\sigma} from the smaller, but also very precise value obtained by the GEM collaboration at COSY.

View original: http://arxiv.org/abs/1207.3710