Measurements of the branching fractions for J/ψ and ψ′→ΛΛ̄π0 and ΛΛ̄η

We report on a study of the isospin-violating and isospin-conserving decays of the J/ψ and ψ′ charmonium state to ΛΛ̅ π0 and ΛΛ̅ η, respectively. The data are based on 225 million J/ψ and 106 million ψ′ events that were collected with the BESIII detector. The most accurate measurement of the branching fraction of the isospin-violating process J/ψ→ΛΛ̅ π0 is obtained, and the isospin-conserving processes J/ψ→ΛΛ̅ η and ψ′→ΛΛ̅ η are observed for the first time. The branching fractions are measured to be B(J/ψ→ΛΛ̅ π0)=(3.78±0.27stat±0.30sys)×10-5, B(J/ψ→ΛΛ̅ η)=(15.7±0.80stat±1.54sys)×10-5 and B(ψ′→ΛΛ̅ η)=(2.48±0.34stat±0.19sys)×10-5. No significant signal events are observed for ψ′→ΛΛ̅ π0 decay resulting in an upper limit of the branching fraction of B(ψ′→ΛΛ̅ π0)<0.29×10-5 at the 90% confidence level. The two-body decay of J/ψ→Σ(1385)0Λ̅ +c.c. is searched for, and the upper limit is B(J/ψ→Σ(1385)0Λ̅ +c.c.)<0.82×10-5 at the 90% confidence level