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 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 (B) over bar (0) -> K-S(0)Lambda(+)(c)(Lambda) over bar (-)(c) decays. The measured mass and width are [2942.3 +/- 4.4(stat.) +/- 1.5(syst.)] MeV/c(2) and [14.8 +/- 8.8(stat.) +/- 2.5(syst.)] MeV, respectively, and the product branching fraction is B((B) over bar (0) -> Xi(c)(2930)(+)(Lambda) over bar (-)(c)) B(Xi(c)(2930)(+) -> (K) over bar (0)(S)Lambda(+)(c)) = [2.37 +/- 0.51(stat.) +/- 0.31 (syst.)] x 10(-4). We also measure B((B) over bar (0) -> (K) over bar (0)(S)Lambda(+)(c)(Lambda) over bar (-)(c)) = [3.99 +/- 0.76(stat.) +/- 0.51(syst.)] x 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)(Lambda) over bar (-)(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. Thesemeasurements are obtained from a sample of (772 +/- 11) x 10(6) B (B) over bar pairs collected at the Upsilon(4S) resonance by the Belle detector at the KEKB asymmetric energy electron-positron collider.