Physical Review Letters 101,10 ( 2008 )
We report the first observation of the decay J/psi -> 3 gamma. The signal has a statistical significance of 6 sigma and corresponds to a branching fraction of B(J/psi -> 3 gamma)=(1.2 +/- 0.3 +/- 0.2)x10(-5), in which the errors are statistical and systematic, respectively. The measurement uses psi(2S)->pi(+)pi(-)J/psi events acquired with the CLEO-c detector operating at the CESR e(+)e(-) collider.
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