New determination of the η transition form factor in the Dalitz decay η→e+e-γ with the Crystal Ball/TAPS detectors at the Mainz Microtron

Aguar-Bartolome, P.; Annand, J. R. M.; Arends, H. J.; Bantawa, K.; Beck, R.; Bekrenev, V.; Berghauser, H.; Braghieri, A.; Briscoe, W. J.; Brudvik, J.; Cherepnya, S.; Codling, R. F. B.; Collicott, C.; Costanza, S.; Denig, A.; Downie, E. J.; Drexler, P.; Fil'Kov, L. V.; Fix, A.; Glazier, D. I.; Gregor, R.; Hamilton, D. J.; Heid, E.; Hornidge, D.; Isaksson, L.; Jaegle, I.; Jahn, O.; Jude, T. C.; Kashevarov, V. L.; Keshelashvili, I.; Kondratiev, R.; Korolija, M.; Kotulla, M.; Koulbardis, A.; Kruglov, S.; Krusche, B.; Lisin, V.; Livingston, K.; Macgregor, I. J. D.; Maghrbi, Y.; Manley, D. M.; Masjuan, P.; Mcgeorge, J. C.; Mcnicoll, E. F.; Mekterovic, D.; Metag, V.; Mushkarenkov, A.; Nefkens, B. M. K.; Nikolaev, A.; Novotny, R.; Ortega, H.; Ostrick, M.; Ott, P.; Otte, P. B.; Oussena, B.; Pedroni, P.; Pheron, F.; Polonski, A.; Prakhov, S.; Robinson, J.; Rosner, G.; Rostomyan, T.; Schumann, S.; Sikora, M. H.; Sober, D. I.; Starostin, A.; Strakovsky, I. I.; Suarez, I. M.; Supek, I.; Tarbert, C. M.; Thiel, M.; Thomas, A.; Unverzagt, M.; Watts, D. P.; Werthmuller, D.; Zehr, F.

doi:10.1103/PhysRevC.89.044608

The Dalitz decay η→e+e-γ has been measured in the γp→ηp reaction with the Crystal Ball and TAPS multiphoton spectrometers, together with the photon-tagging facility at the Mainz Microtron MAMI. The experimental statistic used in this work is one order of magnitude greater than in any previous measurement of η→e+e-γ. The value obtained for the slope parameter Λ-2 of the η transition form factor, Λ-2=(1.95±0.15stat±0.10syst) GeV-2, is in good agreement with recent measurements conducted in η→e+e-γ and η→μ+μ-γ decays, as well as with recent form-factor calculations. The uncertainty obtained in the value of Λ-2 is lower compared to results from previous measurements of the η→e+e-γ decay. © 2014 American Physical Society.