Amplitude analysis and branching fraction measurement of J / ψ → Λ Σ ¯ 0 η + c . c .

Based on a sample of ( 10087 ± 44 ) × 10 6 J / ψ events collected with the BESIII detector, a partial-wave analysis of J / ψ → Λ Σ ¯ 0 η + c . c . is performed for the first time. The dominant contributions are found to be excited Λ states with J P = 1 / 2 − and J P = 1 / 2 + in the η Λ mass spectra. The measured masses and widths are M = 1668.8 ± 3.1 ± 21.2 MeV / c 2 and Γ = 52.7 ± 4.2 ± 17.8 MeV for the Λ ( 1670 ) , and M = 1881.5 ± 16.5 ± 20.3 MeV / c 2 and Γ = 82.4 ± 18.2 ± 8.9 MeV for the Λ ( 1810 ) , respectively. The branching fraction is determined to be B ( J / ψ → Λ Σ ¯ 0 η + c . c . ) = ( 3.44 ± 0.11 ± 0.13 ) × 10 − 5 . The first uncertainties are statistical and the second systematic.