Measurement of B(J/psi->eta_c gamma) at KEDR
V. V. Anashin, V. M. Aulchenko, E. M. Baldin, A. K. Barladyan, A. Yu., Barnyakov, M. Yu. Barnyakov, S. E. Baru, I. Yu. Basok, I. V. Bedny, O. L., Beloborodova, A. E. Blinov, V. E. Blinov, A. V. Bobrov, V. S. Bobrovnikov, A., V. Bogomyagkov, A. E. Bondar, A. R. Buzykaev
TL;DR
This paper reports precise measurements of the eta_c meson mass, width, and the branching fraction of J/psi radiative decay using the inclusive photon spectrum from a large sample of J/psi decays at the KEDR detector.
Contribution
The study provides new, more accurate measurements of eta_c properties and the J/psi to eta_c gamma branching fraction, accounting for asymmetric photon line shapes.
Findings
eta_c mass measured as 2978.1 MeV/c^2
eta_c width measured as 43.5 MeV
Branching fraction B(J/psi->eta_c gamma) is 2.59%
Abstract
We present a study of the inclusive photon spectrum from 6.3 million J/psi decays collected with the KEDR detector at the VEPP-4M e+e- collider. We measure the branching fraction of the radiative decay J/psi -> eta_c gamma, eta_c width and mass. Taking into account an asymmetric photon line shape we obtain: M(eta_c) = (2978.1 +- 1.4 +- 2.0) MeV/c^2, Gamma(eta_c) = (43.5 +- 5.4 +- 15.8) MeV, B(J/psi->eta_c gamma) = (2.59 +- 0.16 +- 0.31)%$.
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