B介子稀有衰變之量測（B→hh, B→ηKπ and B→ηππ)

Abstract

We report improved measurements of branching fractions for B→Kπ, B→ ππ and B → KK decays based on a data sample of 447 million BB pairs collected at the Υ(4S) resonance with the Belle detector at the KEKB e+e- storage ring. This data sample is almost five times larger than the sample previously used. We also report the ratios of partial widths for B →Kπ and ππ decays. The values obtained Rc = 1.08 +- 0.06 +- 0.07 and Rn = 1.07 +- 0.08 +- 0.08 are consistent with Standard Model expectations. Clear signals in B+ → K0K+ and B0 → K0K0 are observed with significances of 5.7 σ and 6.0 σ , respectively. The corresponding branching fractions are measured to be B(B+ → K0K+) = (1.23+0.33-0.28 +- 0.07) x 10-6 and B(B0 → K0K0) = (0.88+0.25-0.21 +- 0.09) x 10-6. We also report their partial rate asymmetries: ACP (B+ → K0K+) = 0.133+0.229-0.240 +- 0.003, ACP (B+ → K0π+) = 0.034+-0.032+-0.001 and ACP (B0 → K0K0) = -0.571+0.719-0.647 +-0.013. No signal is observed in the decay B0 → K+K- and we set an upper limit of 2.5 x 10-7 at 90% confidence level.

We also study the B → ηK+π- and B→ ηπ+π- decays using 386 million BB pairs. The measured branching fractions are B(B0 → ηK+π-)= (31.7 +- 1.9+2.2-2.6) x 10-6, where the first error is statistical error and the second one is systematic error. The possible three-body decay of B0→ ηπ+π- and the possible two-body decays of B0 → a+-0 h-+ with a-0 → ηπ- have also been searched for, where h stands for either kaon or pion. No significant signal has been found and we obtain B(B0 → ηπ+π-) < 11.9 x 10-6, B(B0 → a+-0 K-+ ) x B(a-0 → ηπ-) < 1.6 x 10-6 and B(B0 → a+-0 π-+ ) x B(a-0 → ηπ-) < 2.8 x 10-6 for the 90% C.L. upper limits.