ISSN - 15507998, Physical Review D - Particles, Fields, Gravitation and Cosmology, 2012, vol. 86, p. -
First observation of the isospin violating decay J/ ψ→ΛΣ ̄0+c.c.
Using a sample of (225.2±2.8)×106 J/ψ events collected with the BESIII detector, we present results of a study of J/ ψ→γΛΛ̄ and report the first observation of the isospin violating decay J/ψ→ΛΣ ̄0+c.c., in which Σ ̄0 decays to γΛ̄. The measured branching fractions are B(J/ψ→Λ̄Σ0)=(1.46±0. 11±0.12)×10 -5 and B(J/ ψ→ΛΣ ̄0)=(1.37±0.12±0.11) ×10 -5. We search for Λ(1520)→γΛ decay, and find no evident signal, and an upper limit for the product branching fraction B(J/ψ→ΛΛ̄(1520)+c.c.) ×B(Λ(1520)→γΛ)<4.1×10 -6 is set at the 90% confidence level. We also report the observation of η c→ΛΛ̄ in J/ ψ→γη c, η c→ΛΛ̄ and measure the branching fraction B(η c→ΛΛ̄)=(1.16±0.12(stat) ±0.19(syst)±0.28(PDG))×10 -3. © 2012 American Physical Society.