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 Ξ𝑐(2930)+ with a signal significance of 3.9𝜎 with systematic errors included. The charged Ξ𝑐(2930)+ is found in its decay to 𝐾0𝑆Λ+𝑐 in the substructure of 𝐵¯0→𝐾0𝑆Λ+𝑐Λ¯−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¯0→Ξ𝑐(2930)+Λ¯−𝑐)(Ξ𝑐(2930)+→𝐾¯0Λ+𝑐)=[2.37±0.51(stat.)±0.31(syst.)]×10−4. We also measure (𝐵¯0→𝐾¯0Λ+𝑐Λ¯−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 Λ+𝑐Λ¯−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)×106𝐵𝐵¯ pairs collected at the Υ(4𝑆) resonance by the Belle detector at the KEKB asymmetric energy electron-positron collider.