Determination of the η-transition form factor in the γp→pη→pγe+e- reaction

H. Berghäuser, V. Metag, A. Starostin, P. Aguar Bartolomé, L. K. Akasoy, J. R.M. Annand, H. J. Arends, K. Bantawa, R. Beck, V. Bekrenev, A. Braghieri, D. Branford, W. J. Briscoe, J. Brudvik, S. Cherepnya, B. T. Demissie, E. J. Downie, P. Drexler, M. Dieterle, L. V. Fil'kovA. Fix, D. I. Glazier, E. Heid, D. Hornidge, O. Jahn, T. C. Jude, V. L. Kashevarov, A. Knezevic, R. Kondratiev, M. Korolija, M. Kotulla, A. Koulbardis, S. Kruglov, B. Krusche, B. Lemmer, V. Lisin, K. Livingston, I. J.D. MacGregor, Y. Maghrbi, D. M. Manley, M. Martinez-Fabregate, J. C. McGeorge, E. F. McNicoll, D. Mekterovic, S. Micanovic, A. Mushkarenkov, B. M.K. Nefkens, A. Nikolaev, R. Novotny, M. Ostrick, R. O. Owens, P. Pedroni, F. Pheron, A. Polonski, J. Robinson, S. N. Prakhov, G. Rosner, T. Rostomyan, S. Schumann, D. Sober, I. M. Suarez, I. Supek, C. M. Tarbert, M. Thiel, A. Thomas, M. Unverzagt, D. P. Watts, D. Werthmüller, I. Zamboni, F. Zehr

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40 Citations (Scopus)


The Dalitz decay η→γe+e- has been measured using the combined Crystal Ball and TAPS photon detector setup at the electron accelerator MAMI-C. Compared to the most recent transition form-factor measurement in the e+e- channel, statistics have been improved by one order of magnitude. The e+e- invariant mass distribution shows a deviation from the QED prediction for a point-like particle, which can be described by a form-factor. Using the usual monopole transition form-factor parameterization, F(m2)=(1-m2/Λ2)-1, a value of Λ-2=(1.92±0.35(stat)±0.13(syst)) GeV-2 has been determined. This value is in good agreement with a recent measurement of the η Dalitz decay in the μ+μ- channel and with recent form-factor calculations. An improved value of the branching ratio BR(η→γe+e-)=(6.6±0.4(stat)±0.4(syst)).10-3 has been determined.

Original languageEnglish
Pages (from-to)562-567
Number of pages6
JournalPhysics Letters, Section B: Nuclear, Elementary Particle and High-Energy Physics
Issue number5
Publication statusPublished - 27 Jul 2011


  • Meson decays
  • Transition form factor

ASJC Scopus subject areas

  • Nuclear and High Energy Physics

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