Evidence for eta(c) -> gamma gamma and measurement of J/psi -> 3 gamma
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KünyeAblikim, M., Achasov, M. N., Ambrose, D. J., An, F. F., An, Q., An, Z. H. ... BESIII Collaboration. (2013). Evidence for eta(c) -> gamma gamma and measurement of J/psi -> 3 gamma. Physical Review D, 87 (3). http://dx.doi.org/10.1103/PhysRevD.87.032003.
The decay of J/psi to three photons is studied using psi (3686) -> pi(+) pi(-) J/psi in a sample of 1.0641 X 10(8) psi (3686) events collected with the BESIII detector. Evidence of the direct decay of eta(c) to two photons, eta(c) -> gamma gamma, is reported, and the product branching fraction is determined to be B(J/psi -> gamma eta(c,) eta(c) -> gamma gamma = (4.5 +/- 1.2 +/- 0.6) X 10(-6), where the first error is statistical and the second is systematic. The branching fraction for J/psi -> 3 gamma is measured to be (11.3 +/- 1.8 +/- 2.0) X 10(-6) with improved precision.