Observation of the Electromagnetic Radiative Decays of the Λ(1520) and Λ(1690) to γΣ^{0}

Using (10087±44)×10^{6}  J/ψ events collected with the BESIII detector, we present a study of resonant structures in the J/ψ→ΛΛ[over ¯]γ and ΛΣ[over ¯]^{0}γ processes, reporting the first observation of the electromagnetic radiative decays of the Λ(1520) and Λ(1690) to γΣ^{0}, with a statistical significance of 16.6σ and 23.2σ, respectively. The ratio of the branching fractions {B[Λ(1520)→γΛ]/B[Λ(1520)→γΣ^{0}]} is determined to be 3.19±0.34(stat)±0.19(syst), which is in agreement with flavor SU(3) symmetry within two standard deviations. The branching fraction of Λ(1520)→γΣ^{0} is measured to be B[Λ(1520)→γΣ^{0}]=[2.66±0.28(stat)±0.50(syst)]×10^{-3}, corresponding to a partial width of Γ[Λ(1520)→γΣ^{0}]=[46.8±6.6(stat)±9.3(syst)]  keV, which is inconsistent with predictions from the relativized constituent quark model and the Algebraic model. Additionally, we observe a clear resonant structure in the γΣ^{0} mass spectrum near 1.7  GeV/c^{2}, attributed to the Λ(1690). The product branching fraction B[J/ψ→Λ[over ¯]Λ(1690)+c.c.]×B[Λ(1690)→γΣ^{0}] is measured for the first time as [6.05±0.42(stat)±0.39(syst)]×10^{-6}. However, no corresponding structure is seen in the γΛ mass spectrum, so an upper limit on the product branching fraction B[J/ψ→Λ[over ¯]Λ(1690)+c.c.]×B[Λ(1690)→γΛ] is determined to be 5.08×10^{-7} at the 90% confidence level.