Evidence of a structure in $$\bar{K}^{0} \Lambda _{c}^{+}$$ K¯0Λc+ consistent with a charged $$\Xi _c(2930)^{+}$$ Ξc(2930)+ , and updated measurement of $$\bar{B}^{0} \rightarrow \bar{K}^{0} \Lambda _{c}^{+} \bar{\Lambda }_{c}^{-}$$ B¯0→K¯0Λc+Λ¯c- at Belle

Abstract

Abstract We report evidence for the charged charmed-strange baryon $$\Xi _{c}(2930)^+$$ Ξc(2930)+ with a signal significance of 3.9$$\sigma $$ σ with systematic errors included. The charged $$\Xi _{c}(2930)^+$$ Ξc(2930)+ is found in its decay to $$K_{S}^{0} \Lambda _{c}^+$$ KS0Λc+ in the substructure of $$\bar{B}^{0} \rightarrow K^{0}_{S} \Lambda _{c}^{+} \bar{\Lambda }_{c}^{-}$$ B¯0→KS0Λc+Λ¯c- decays. The measured mass and width are $$[2942.3 \pm 4.4 ({\mathrm{stat.}}) \pm {1.5}({\mathrm{syst.}})]$$ [2942.3±4.4(stat.)±1.5(syst.)] MeV/$$c^{2}$$ c2 and $$[14.8 \pm 8.8({\mathrm{stat.}}) \pm {2.5}({\mathrm{syst.}})]$$ [14.8±8.8(stat.)±2.5(syst.)] MeV, respectively, and the product branching fraction is $$\mathcal{B}(\bar{B}^{0} \rightarrow \Xi _c(2930)^{+} \bar{\Lambda }_{c}^{-}) \mathcal{B}(\Xi _c(2930)^{+}\rightarrow \bar{K}^{0} \Lambda _{c}^{+})=[2.37 \pm 0.51 ({\mathrm{stat.}})\pm 0.31({\mathrm{syst.}})]\times 10^{-4}$$ B(B¯0→Ξc(2930)+Λ¯c-)B(Ξc(2930)+→K¯0Λc+)=[2.37±0.51(stat.)±0.31(syst.)]×10-4 . We also measure $$\mathcal{B}(\bar{B}^{0} \rightarrow \bar{K}^{0} \Lambda _{c}^{+} \bar{\Lambda }_{c}^{-}) = [3.99 \pm 0.76({\mathrm{stat.}}) \pm 0.51({\mathrm{syst.}})] \times 10^{-4}$$ B(B¯0→K¯0Λc+Λ¯c-)=[3.99±0.76(stat.)±0.51(syst.)]×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, $$Y_{\eta }$$ Yη , in the $$\Lambda _{c}^{+}\bar{\Lambda }_{c}^{-}$$ Λc+Λ¯c- invariant mass spectrum. No clear signals of the Y(4660) or $$Y_{\eta }$$ Yη 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 $$(772\pm 11)\times 10^{6} B\bar{B}$$ (772±11)×106BB¯ pairs collected at the $$\Upsilon (4S)$$ Υ(4S) resonance by the Belle detector at the KEKB asymmetric energy electron-positron collider.