We study the charmless decays B -> Lambda(Lambda) over barh , where h stands for pi(+), K+, K-0, K*(+), or K*(0), using a 605 fb(-1) data sample collected at the Gamma(4S) resonance with the Belle detector at the KEKB asymmetric energy e(+)e(-) collider. We observe B-0 -> Lambda(Lambda) over barK(0) and B-0 -> Lambda(Lambda) over barK*(0) with branching fractions of (4.76(-0.68)(+0.84) (stat) +/- 0. 61 (syst)) x 10(-6) and (2.46(-0.72)(+0.87) +/- 0.34) x 10(-6), respectively. The significances of these signals in the threshold-mass enhanced mass region, M Lambda(Lambda) over bar < 2.85 GeV / c(2), are 12.4 sigma and 9.3 sigma, respectively. We also update the branching fraction B(B+ -> LambdaK+) = (3.38(-0.36)(+0.41) +/- 0.41) x 10(-6) with better accuracy, and report the following measurement or 90% confidence level upper limit in the threshold-mass-enhanced region: B(B+ -> Lambda(Lambda) over barK*(+)) = (2.19(-0.88)(+1.13) +/- 0.33) x 10(-6) with 3.7 sigma significance; B(B+ -> Lambda(Lambda) over bar pi(+)) < 0.94) x 10(-6). A related search for B-0 -> Lambda(D) over bar0 yields a branching fraction B(B-0 -> Lambda(Lambda) over bar(D) over bar (0)) = (1.05(-0.44)(+0.57) +/- 0.14) x 10(-5). This may be compared with the large, similar to 10(-4), branching fraction observed for B-0 -> p (p) over bar(D) over bar (0). . The M Lambda(Lambda) over bar enhancements near threshold and related angular distributions for the observed modes are also reported.
Olivier Schneider, Yiming Li, Mingkui Wang, Chao Wang, Sun Hee Kim, Donghyun Kim, Xiao Wang, Lei Li
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