B介子衰變至p pbar K/π之研析與尋找B->πll衰變

Abstract

B+->p‾pK+ and B+->p‾pπ+ We study the characteristics of the low mass p‾p enhancement near threshold in the baryonic B decays: B+->p‾pK+ and B+->p‾pπ+. We observe that the proton polar angle distributions in the p‾p helicity frame in the two decays have the opposite polarity, and measure the forward-backward asymmetries as a function of the p‾p mass for the p‾pK+ mode. We also search for the intermediate two-body decays, B+->‾p ++ and B+->p‾ 0, and set upper limits on their branching fractions: B(B+->‾p ++) < 0.14 × 10^-6 and B(B+->p‾ 0) < 1.38×10^-6. These results are obtained from a data sample of 449 million BB pairs collected near the Upsilon(4S) resonance with the Belle detector at KEKB. B+->p‾Λγ, p‾Λπ0 and B0->p‾Λπ− To further understand the mechanism in the low p‾p mass for baryonic B decays. We review the study of B+->p‾Λγ, p‾Λπ0 and B0->p‾Λπ− done by Y.-J. Lee (NTUHEP group) in 2006. The branching fractions and angular distributions of the three decays are remeasured with the same data sample, and the results are consistent with Lee’s study. In adition, we also measure the anisotropy parameter ‾α of the secondary proton from decays. The results are ‾α(B+->p‾Λγ) = −0.57 ± 0.33(stat) ± 0.10(syst), ‾α(B+->p‾Λπ0) = −0.27 ± 0.33(stat) ± 0.10(syst), and ‾α(B+->p‾Λπ−) = −0.28 ± 0.21(stat) ± 0.10(syst). B->πℓ+ℓ− We also present a search for the B+->π+ℓ+ℓ− and B0->π0ℓ+ℓ− decays, with a data sample of 657 million BB pairs. By performing maximum likelihood fits to the reconstructed candidates, no significant signal is observed and we set the upper limit on the isospin-averaged branching fraction B(B->πℓ+ℓ−) < 6.2 × 10^-8 at the 90% confidence level.