Abstract The decays of J / ψ and ψ ( 2 S ) to n K S 0 Λ ¯ + c.c. are observed and measured for the first time, and the perturbative QCD “12%” rule is tested, based on 5.8 × 10 7 J / ψ and 1.4 × 10 7 ψ ( 2 S ) events collected with BESII detector at the Beijing Electron–Positron Collider. No obvious enhancement near n Λ ¯ threshold in J / ψ → n K S 0 Λ ¯ + c.c. is observed, and the upper limit on the branching ratio of J / ψ → K S 0 X , X → n Λ ¯ is determined.
