Evidence of a structure in ${\bar{K}}^0{\Lambda }_c^{+}$ consistent with a charged ${\Xi }_c(2930{)}^{+}$, and updated measurement of ${\bar{B}}^0\to {\bar{K}}^0{\Lambda }_c^{+}{\bar{\Lambda }}_c^{-}$ at Belle

Abstract

We report evidence for the charged charmed-strange baryon ${\Xi }_c(2930{)}^{+}$ with a signal significance of 3.9$\sigma$ with systematic errors included. The charged ${\Xi }_c(2930{)}^{+}$ is found in its decay to $K_S^0{\Lambda }_c^{+}$ in the substructure of ${\bar{B}}^0\to K_S^0{\Lambda }_c^{+}{\bar{\Lambda }}_c^{-}$ decays. The measured mass and width are $[2942.3\pm 4.4(stat.)\pm 1.5(syst.)]$~MeV/$c^2$ and $[14.8\pm 8.8(stat.)\pm 2.5(syst.)]$~MeV, respectively, and the product branching fraction is $\mathcal{B}({\bar{\mathcal{B}}}^0\to {\Xi }_c(2930{)}^{+}{\bar{\Lambda }}_c^{-})\mathcal{B}({\Xi }_c(2930{)}^{+}\to {\bar{\mathcal{K}}}^0{\Lambda }_c^{+})=[2.37\pm 0.51(stat.)\pm 0.31(syst.)]\times 10^{-4}$. We also measure $\mathcal{B}({\bar{\mathcal{B}}}^0\to {\bar{\mathcal{K}}}^0{\Lambda }_c^{+}{\bar{\Lambda }}_c^{-})=[3.99\pm 0.76(stat.)\pm 0.51(syst.)]\times 10^{-4}$ with greater precision than previous experiments, and present the results of a search for the charmonium-like state $Y(4660)$ and its spin partner, $Y_{\eta }$, in the ${\Lambda }_c^{+}{\bar{\Lambda }}_c^{-}$ invariant mass spectrum. No clear signals of the $Y(4660)$ or $Y_{\eta }$ are observed and the 90\% credibility level (C.L.) upper limits on their production rates are determined. These measurements are obtained from a sample of $(772\pm 11)\times 10^{6}B\bar{B}$ pairs collected at the ${\rm Y}(4S)$ resonance by the Belle detector at the KEKB asymmetric energy electron-positron collider.

Comments: 8 pages, 5 figures