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.
|Number of pages||6|
|Journal||Physics Letters, Section B: Nuclear, Elementary Particle and High-Energy Physics|
|Publication status||Published - 27 Jul 2011|
- Meson decays
- Transition form factor
ASJC Scopus subject areas
- Nuclear and High Energy Physics