Evidence forηc→γγand measurement ofJ/ψ→3γ

M. Ablikim, M. N. Achasov, D. J. Ambrose, F. F. An, Q. An, Z. H. An, J. Z. Bai, Y. Ban, J. Becker, J. V. Bennett, M. Bertani, J. M. Bian (+333 others)
2013 Physical Review D  
The decay of J/ψ to three photons is studied using ψ(3686)→π^+π^-J/ψ in a sample of 1.0641×10^8 ψ(3686) events collected with the BESIII detector. Evidence of the direct decay of η_c to two photons, η_c→γγ, is reported, and the product branching fraction is determined to be B(J/ψ→γη_c,η_c→γγ)=(4.5±1.2±0.6)×10^-6, where the first error is statistical and the second is systematic. The branching fraction for J/ψ→3γ is measured to be (11.3±1.8±2.0)× 10^-6 with improved precision.
doi:10.1103/physrevd.87.032003 fatcat:pgrsd7hjfjcfdox3j3buuady3e