臺灣博碩士論文加值系統

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.

Introduction 1
1.1 Motivation . . . . . . . . . . . . . . . . . . . . . . 1
1.2 Quark model . . . . . . . . . . . . . . .. . . . .. . 2
1.2.1 Quantum numbers of the quarks . . .. 2
1.2.2 Mesons . . . . . . . . . . . . . . . . . . . . .. . .. 2
1.2.3 Exotic mesons . . . . . . . . . . . . . . . . . . 3
1.3 The Cabibbo-Kobayashi-Maskawa quark-mixing matrix . . 4
1.4 B→hh . . . . . . . . . . . . . . . . . . . .. . . . . . 6
1.4.1 Final state interactions . . . . . . . . . . . . 6
1.4.2 Perturbative QCD . . . . . . . . . . . . . . 11
1.5 B0 →a+0 π- and B0→a+0 K- decays . . . 13
1.5.1 Physical properties of a0 . . . . . . . . . 15
1.5.2 B→a0(980)K and a0(980)π decays . . 15
1.5.3 B →a0(1450)K, a0(1450) π decays . . 17
2 KEK B-Factory and Belle Detector 19
2.1 KEK B-Factory . . . . . . . . . . . . . . . . . . 19
2.2 Belle Detector . . . . . . . . . . . . . . . . . . . 20
2.2.1 Beam-line Magnets near the Interaction Point . . 21
2.2.2 Extreme Forward Calorimeter, EFC . . . 22
2.2.3 Silicon Vertex Detector, SVD . . . . . . 25
2.2.4 Central Drift Chamber, CDC . . . . . . . . 27
2.2.5 Aerogel ^Cerenkov Counter System, ACC . . 28
2.2.6 Time-of-Flight Counters, TOF . . .. . . . 29
2.2.7 Electromagnetic Calorimeter, ECL . .. . 30
2.2.8 Particle Identification of Electrons and Charged Kaons, EID and KID ...31
2.2.9 KL and Muon Detection System, KLM . . 33
3 Data sample and Event Selection 35
3.1 Data sample . . . . . . . . . . . . . . . 35
3.1.1 B→ηKπ and B→ηππ. . .. . . . . . . 35
3.1.2 B→hh . . . . . . . . . . . . . . . . . .. . . . . 35
3.2 Event selection . . . . . . . . . . .. . . . . . . 35
3.2.1 Particle identification . . . . . . . . .. . . 35
3.2.2 Hadron B skim . . . . . . . . . . . . . . . . 37
3.2.3 Event selection . . . . . . . . . . . . . . . . 40
3.2.4 Event shape variables . . . . . . . .. . . . 42
3.3 Continuum background suppression . 48
3.3.1 B→hh . . . . . . . . . . . . . . . . . . . . . . . 48
3.3.2 B→ηKπ and B→ηππ . . . . . . . . . 50
3.4 Likelihood ratio cuts optimization . . . 51
3.4.1 B→hh . . . . . . . . . . . . . . . . . . .. . . . 52
3.4.2 B→ηKπ and B→ηππ . . . . . . . . . 54
4 Signal Extraction 57
4.1 Signal shape . . . . . . . . . . . . . . . . . . . 57
4.2 Consistency Check . . . . . . . . . . .. . . . 57
4.2.1 B→hh . . . . . . . . . . . . . . . . . . . . . . 57
4.2.2 B→ηKπ and B→ηππ . . . . . . . . . 62
4.3 Mbc and ΔE PDF of Background . . 63
4.3.1 B→hh . . . . . . .. . . . . . . . . . . . . . . 63
4.3.2 B→ηhh . . . . . . . . . . . . . . . . . . . . . 63
5 Fitting Method and Results 73
5.1 Maximum Likelihood fit . . . . . . . . . 73
5.1.1 B→hh . . . . . . . . . . . . . . . . . . . . . 74
5.1.2 B→ηKπ and B→ηππ . . . . . . . 74
5.2 Fitting results . . . . . . . . . . . . . . . . . . 74
5.2.1 B→hh . . . . . . . . . . . . . . . . .. . . . . 74
5.2.2 B→ηKπ and B→ηππ . . . . . . . . 80
5.3 2-Body Intermediate States of B→ηhh . 83
5.3.1 Two Body Mass spectra of ηK+π- in the final state . . 83
5.3.2 Two Body Mass spectra of ηπ+π- in the final state . . . 83
5.3.3 B0→a-0 K+ . . . . . . . . . . . . . . . . 83
5.3.4 B0→a+-π0. . . . . . . . . . . . . . . . 84
6 Systematics and Efficiency Correction 89
6.1 Tracking efficiency and systematic error . . 89
6.1.1 η→π+π-π0 mode . . . . . . . . . . . . 89
6.1.2 η→γγmode . . . . . . . . . . . . . . . . . 90
6.1.3 Partial decays of the D* meson . . 91
6.2 π0efficiency and systematic error . . 94
6.2.1 η→γγdecay . . . . . . . . . . . . . . . . . 95
6.2.2 η→3π0 . . . . . . . . . . . . . . . . . .. . . 95
6.2.3 KS reconstruction efficiency . . . . 97
6.3 PID performance . . . . . . . . . . . . . . . 97
6.4 Systematics . . . . . . . . . . . . . . . . . . . 100
6.5 Reconstruction efficiency . . . . . . . . 102
6.5.1 Reconstruction efficiency of B→hh . 102
6.5.2 Reconstruction efficiency of B→ ηhh 103
iii 7 Summary and Conclusion 107
7.1 B→ hh . . . . . . . . . . . . . . . . . . .. . . . 107
7.2 B→ ηhh . . . . . . . . . . . . . . . . . . . . . 109

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