Measurements of J/ψ and ψ(2S) decays into ΛΛ¯π0 and ΛΛ¯η

Using 58x10(6) J/psi and 14x10(6) psi(2S) events collected by the BESII detector at the BEPC, branching fractions or upper limits for the decays J/psi and psi(2S)->Lambda(Lambda) over bar pi(0) and Lambda(Lambda) over bar eta are measured. For the isospin violating decays, the upper limits are determined to be B(J/psi ->Lambda(Lambda) over bar pi(0))< 6.4x10(-5) and B[psi(2S)->Lambda(Lambda) over bar pi(0)]< 4.9x10(-5) at the 90% confidence level. The isospin conserving process J/psi ->Lambda(Lambda) over bar eta is observed for the first time, and its branching fraction is measured to be B(J/psi ->Lambda(Lambda) over bar eta)=(2.62 +/- 0.60 +/- 0.44)x10(-4), where the first error is statistical and the second one is systematic. No Lambda(Lambda) over bar eta signal is observed in psi(2S) decays, and B[psi(2S)->Lambda(Lambda) over bar eta]< 1.2x10(-4) is set at the 90% confidence level. Branching fractions of J/psi decays into Sigma(+)pi(-)(Lambda) over bar and Sigma(-)pi(+)Lambda are also reported, and the sum of these branching fractions is determined to be B(J/psi ->Sigma(+)pi(-)(Lambda) over bar +c.c.)=(1.52 +/- 0.08 +/- 0.16)x10(-3).