Amplitude analysis and branching fraction measurement of $J/\psi \to \Lambda\bar{\Sigma}^0\eta +\mathrm{c.c}$

Abstract

Based on a sample of $(10087\pm44)\times10^{6}$ $J/\psi$ events collected with the BESIII detector, a partial-wave analysis of $ J/\psi \to \Lambda \bar{ \Sigma }^0\eta +\mathrm{c.c} $ is performed for the first time. The dominant contributions are found to be excited $\Lambda$ states with $J^P=1/2^-$ and $J^P=1/2^+$ in the $\eta\Lambda$ mass spectra. The measured masses and widths are $M=1668.8\pm3.1\pm21.2$ MeV/$c^2$ and $\Gamma=52.7\pm4.2\pm17.8$ MeV for the $\Lambda(1670)$, and $M=1881.5\pm16.5\pm20.3$ MeV/$c^2$ and $\Gamma=82.4\pm18.2\pm8.9$ MeV for the $\Lambda(1810)$, respectively. The branching fraction is determined to be $ \mathcal{B}(J/\psi \to \Lambda \bar{ \Sigma }^0\eta +\mathrm{c.c}) $ = $(3.44 \pm 0.11 \pm 0.13) \times 10^{-5}$. The first uncertainties are statistical and the second systematic.