Observation of the decay ${\chi }_{cJ}\to {\mathrm{\Omega }}^{-}{\overline{\mathrm{\Omega }}}^{+}$

Using an $e^{+}{e}^{-}$ collision data sample of $(27.08\pm 0.14)\times {10}^8\psi (3686)$ events collected by the BESIII detector, we report the first observation of ${\chi }_{cJ}\to {\mathrm{\Omega }}^{-}{\overline{\mathrm{\Omega }}}^{+}$ ($J=0$, 1, 2) decays with significances of $5.6\sigma$, $6.4\sigma$, and $18\sigma$, respectively, where the ${\chi }_{cJ}$ mesons are produced in the radiative $\psi (3686)$ decays. The branching fractions are determined to be $\mathcal{B}({\chi }_{c0}\to {\mathrm{\Omega }}^{-}{\overline{\mathrm{\Omega }}}^{+})=(3.51\pm 0.54\pm 0.29)\times {10}^{-5}$, $\mathcal{B}({\chi }_{c1}\to {\mathrm{\Omega }}^{-}{\overline{\mathrm{\Omega }}}^{+})=(1.49\pm 0.23\pm 0.10)\times {10}^{-5}$, and $\mathcal{B}({\chi }_{c2}\to {\mathrm{\Omega }}^{-}{\overline{\mathrm{\Omega }}}^{+})=(4.52\pm 0.24\pm 0.18)\times {10}^{-5}$, where the first and second uncertainties are statistical and systematic, respectively.

Figure 1

Recoil mass $R{M}_{{\mathrm{\Omega }}^{-}}$. The blue dotted line histogram is from the signal MC samples of ${\chi }_{c0,1,2}\to {\mathrm{\Omega }}^{-}{\overline{\mathrm{\Omega }}}^{+}$, where the proportions of the three signal channels are distributed according to the measured BFs from this study. The red solid line histogram is from the MC sample of background $\psi (3686)\to {\mathrm{\Omega }}^{-}{\overline{\mathrm{\Omega }}}^{+}$ decays, and the black arrow denotes the chosen $R{M}_{{\mathrm{\Omega }}^{-}}$ requirement. The normalization between the signal MC and background MC samples is arbitrary.

Figure 2

Fit to the $R{M}_{\gamma }$ distribution of the accepted candidates in data. The dots with error bars are data, the blue solid line is the total fit, the green short dashed line represents the fitted combinatorial background shape, and the red long dashed, dark brown short dot-dashed and magenta long dot-dashed lines indicate the ${\chi }_{c0}$, ${\chi }_{c1}$, and ${\chi }_{c2}$ signals, respectively.