Evidence of a structure in K¯0Λc+ consistent with a charged Ξ c(2930) + , and updated measurement of B¯0→K¯0Λc+Λ¯c- at Belle: Belle Collaboration

Abstract

We report evidence for the charged charmed-strange baryon Ξ c(2930) + with a signal significance of 3.9σ with systematic errors included. The charged Ξ c(2930) + is found in its decay to KS0Λc+ in the substructure of B¯0→KS0Λc+Λ¯c- decays. The measured mass and width are [2942.3 ± 4.4 (stat.) ± 1.5 (syst.)] MeV/c2 and [14.8 ± 8.8 (stat.) ± 2.5 (syst.)] MeV, respectively, and the product branching fraction is 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 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, Yη, in the Λc+Λ¯c- invariant mass spectrum. No clear signals of the Y(4660) or 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 ± 11) × 10 6BB¯ pairs collected at the Υ (4 S) resonance by the Belle detector at the KEKB asymmetric energy electron-positron collider.