| Summary: | 碩士 === 國立臺灣大學 === 物理研究所 === 96 === In the study of B → Λ Λbar h, where h stands for π+, K+, K0 ,K∗+, or K∗0, we observe the charmless decays B0 → Λ Λbar K0 and B0 → Λ Λbar K∗0 with a branching fraction of (4.76{+0.84 −0.68(stat.)} ± 0.60(syst.)) × 10−6 and (2.46{+0.87 −0.72(stat.)} ± 0.34(syst.)) × 10−6, respectively. The statistical significance is 12.4σ and
9.4σ for the signal in the low M(ΛΛbar) region. We also report the following branching fractions or 90% confidence level upper limits: B(B+ → Λ Λbar K+) = (3.38{+0.41 −0.36}±0.41)×10−6, B(B+ → Λ Λbar π+) < 0.94×10−6 in M(ΛΛbar) < 2.85 GeV/c2 region, B(B+ → Λ Λbar K∗+) < 5.01 × 10−6 in M(ΛΛbar) < 2.85 GeV/c2 region, and B(B0 → Λ Λbar D0) < 2.73 × 10−5 in whole M(ΛΛbar) region. The important characteristics of the low M(ΛΛbar) enhancements near threshold and the related angular distributions for the observed modes are presented. These results are obtained from a 605 fb−1 data sample collected near the Upsilon(4S) resonance with the Belle detector at the KEKB asymmetric energy e+e− collider.
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