Abstract
We report the first observation of the Xi _{c}(2930)^0 charmed-strange baryon with a significance greater than 5sigma . The Xi _{c}(2930)^0 is found in its decay to K^- Lambda _{c}^+ in B^{-} rightarrow K^{-} Lambda _{c}^{+} bar{Lambda }_{c}^{-} decays. The measured mass and width are [2928.9 pm 3.0(mathrm stat.)^{+0.9}_{-12.0}(mathrm syst.)] MeV/c^{2} and [19.5 pm 8.4(mathrm stat.) ^{+5.9}_{-7.9}(mathrm syst.)] MeV, respectively, and the product branching fraction is mathcal{B}(B^{-} rightarrow Xi _{c}(2930)^0 bar{Lambda }_{c}^{-}) mathcal{B}(Xi _{c}(2930)^0 rightarrow K^- Lambda _{c}^{+})=[1.73 pm 0.45(mathrm stat.) pm 0.21(mathrm syst.)]times 10^{-4}. We also measure mathcal{B}(B^{-} rightarrow K^{-} Lambda _{c}^{+} bar{Lambda }_{c}^{-}) = [4.80 pm 0.43(mathrm stat.) pm 0.60(mathrm syst.)] times 10^{-4} with improved precision, and 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) nor its spin partner 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 (772pm 11)times 10^{6} Bbar{B} pairs collected at the Upsilon (4S) resonance by the Belle detector at the KEKB asymmetric energy electron–positron collider.
Highlights
Credibility level (C.L.) upper limits on their production rates are determined
Observe the c(2930)0 signal with a significance of 5.1σ. This analysis is based on the full data sample collected at the Υ(4S) resonance by the Belle detector [21,22] at the KEKB asymmetric energy electron–positron collider [23,24]
Simulated signal events with B meson decays are generated using EvtGen [25], while the inclusive decays are generated via PYTHIA [26]
Summary
Received: 25 January 2018 / Accepted: 8 March 2018 / Published online: 23 March 2018
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