First observation of J/ψJ/ψ and ψ(2S)ψ(2S) decaying to nKS0Λ¯+c.c.

The decays of J/ψJ/ψ and ψ(2S)ψ(2S) to nKS0Λ¯+c.c. are observed and measured for the first time, and the perturbative QCD “12%” rule is tested, based on 5.8×1075.8×107J/ψJ/ψ and 1.4×1071.4×107ψ(2S)ψ(2S) events collected with BESII detector at the Beijing Electron–Positron Collider. No obvious enhancement near nΛ¯ threshold in J/ψ→nKS0Λ¯+c.c. is observed, and the upper limit on the branching ratio of J/ψ→KS0X,X→nΛ¯ is determined.