Measurement of branching ratios for ηc hadronic decays

Abstract In a sample of 58 million J / ψ events collected with the BES II detector, the process J / ψ → γη c is observed in five decay channels: η c → K + K − π + π − , π + π − π + π − , K ± K 0 S π ∓ (with K 0 S → π + π − ), φφ (with φ → K + K − ) and p p . From these signals, we determine Br(J/ψ→γη c )Br(η c →K + K − π + π − )=(1.5±0.2±0.2)×10 −4 , Br(J/ψ→γη c )Br(η c →π + π − π + π − )=(1.3±0.2±0.4)×10 −4 , Br(J/ψ→γη c )Br(η c →K ± K S 0 π ∓ )=(2.2±0.3±0.5)×10 −4 , Br(J/ψ→γη c )Br(η c →φφ)=(3.3±0.6±0.6)×10 −5 , Br(J/ψ→γη c )Br(η c →p p )=(1.9±0.3±0.3)×10 −5 .