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研究生:吳姿瑩
研究生(外文):Tzu-Ying Wu
論文名稱:中性 B 介子至強子二體稀有衰變之分支比與電荷宇稱不對稱性測量
論文名稱(外文):Measurements of Branching Fractions and CP Asymmetries in Charmless Hadronic Two-body Neutral-B Meson Decays
指導教授:張寶棣
指導教授(外文):Pao-Ti Chang
口試委員:王名儒侯維恕熊怡張敏娟
口試日期:2011-06-02
學位類別:碩士
校院名稱:國立臺灣大學
系所名稱:物理研究所
學門:自然科學學門
學類:物理學類
論文種類:學術論文
論文出版年:2011
畢業學年度:99
語文別:英文
論文頁數:148
中文關鍵詞:分支比電荷宇稱之不對稱性KEKBBelle偵測器B介子
外文關鍵詞:branching fractioncharge asymmetryKEKBBelle detectorB meson
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本論文中,我們收集了 772 百萬 BB 介子對,量測 B0
介子衰變至 K+π−, π+π−, K+K−, K0K0, K0π0 的分支比
及電荷宇稱之不對稱性。藉由 KEKB 不對稱能量電子正子
對撞機在 Υ(4S) 能量下,以及日本國家高能加速器中心
B 介子工廠 Belle 偵測器所收集之資料,進行量測。除了
B0 → K+K− 的衰變未有明顯訊號,其他衰變皆以大於 6
個標準差的信心水準觀測到其衰變。我們量測到其分支比
為: B(B0 → K+π−) = (20.0 ± 0.3(統計誤差)±0.6(系統誤
差)) ×10−6, B(B0 → π+π−) = (5.0 ± 0.2 ± 0.2) ×10−6,
B(B0 → K0K0) = (1.23+0.18 ± 0.03) ×10−6,以及 B(B0 → −0.17
K0π0) = (9.6 ± 0.45 ± 0.46) ×10−6,另外 B0 → K+K− 衰 變未量測到明顯訊號,我們給予 90% 信心水準的分支比上 限 1.5 × 10−7。我們也量測到 K+π− 的電荷宇稱之不對稱性
−0.063 ± 0.014+0.003。

We present the final-update on the measurements of branching
fractionsforneutralBmesondecays,B0 →K+π−,π+π−,K+K−
, K0K0, K0π0, and the measurement of the direct CP violating
partial-rateasymmetriesACP inB0 →K+π−,π+π−,K0K0,K0π0
based on a data sample of 772 × 106BB pairs collected with the
Belle detector at the KEKB energy-asymmetric e+e− collider op-
erating on the Υ(4S) resonance. The data sample is around 1.7
times larger than the sample previous reported. The correspond-
ing branching fractions are to be B(B0 → K+π−) = (20.0 ±
0.3(stat.) ± 0.6(syst.)) ×10−6, B(B0 → π+π−) = (5.0 ± 0.2 ±
0.2) ×10−6, B(B0 → K0K0) = (1.23+0.18 ± 0.03) ×10−6, and −0.17
B(B0 → K0π0) = (9.6 ± 0.45 ± 0.46) ×10−6. The correspond- ing partial-rate asymmetries are ACP (B0 → K+π−) = −0.063 ± 0.014, ACP (B0 → π+π−) = 0.364±0.090, ACP (B0 → K0K0) = −0.362 ± 0.428, and ACP (B0 → K0π0) = 0.010 ± 0.130. The ratio of partial widths Rn for B0 → K+π− and K0π0 decays is Rn = 1.05 ± 0.05 ± 0.08 consistent with the expectation of Stan- dard Model. There is no signal observed for B0 → K+K− decay, and an upper limit of 1.5 × 10−7 on the branching fraction is set at 90% confidence level.

1 introduction 1
1.1 ElementaryParticlePhysics .................... 2
1.2 TheStandardModel ........................ 4
1.2.1 CPViolation ........................ 6
1.2.2 CKMmatrix ........................ 7
1.3 Υand B Mesons .......................... 8
1.4 Motivation..............................9
1.4.1 FinalStateInteractions................... 12
1.4.2 PerturbativeQCD...................... 15
2 KEK-B Factory and Belle Detector 17
2.1 KEKBAccelerator ......................... 17
2.2 BelleDetector............................ 20
2.2.1 BeamPipe ......................... 23
2.2.2 SiliconVertexDetector(SVD)............... 24
2.2.3 ExtremeForwardCalorimeter(EFC) . . . . . . . . . . . 27
2.2.4 CentralDriftChamber(CDC) ............... 28
2.2.5 AerogelC ̆herenkovCounter(ACC) . . . . . . . . . . . . 32
2.2.6 TimeofFlight(TOF).................... 34
2.2.7 Electromagnetic Calorimeter (ECL) . . . . . . . . . . . . 35
2.2.8 SolenoidandIronYoke................... 38
2.2.9 KLandMuonDetector(KLM) .............. 39
3 Basic Selection and B Reconstruction 43
3.1 Datasample............................. 43
3.2 GenerateMonteCarlo........................ 44
3.3 SelectionCriteria .......................... 44
3.3.1 ChargedParticleselection ................. 44
3.3.2 K/πSeparationande,μrejection . . . . . . . . . . . . . 45
3.3.3 π0reconstruction...................... 46
3.3.4 K0reconstruction ..................... 47
3.4 Bmesoncandidates......................... 48
4 Background Study 53
4.1 ContinuumBackgroundDiscrimination . . . . . . . . . . . . . . 53
4.1.1 EventShapeVariables ................... 54
4.1.2 FisherDiscriminantF ................... 56
4.1.3 LikelihoodRatio ...................... 57
4.1.4 LRTranslation....................... 64
4.2 BBBackground .......................... 65
4.2.1 GenericBBackground................... 65
4.2.2 RareBBackground .................... 66
5 Signal Extraction 73
5.1 MaximumLikelihoodfit ...................... 73
5.2 BestBmesoncandidate ...................... 73
5.3 PDFModeling ........................... 74
5.4 KIDOptimizationforB0→K+K−decay ............ 78
5.5 TheCorrelationCheckofhhmode................. 81
5.6 PDFcalibrationwithControlSample. . . . . . . . . . . . . . . . 86
5.7 Consistency Check of 3D fit with Control Sample, B+→D0π+(D0 → K+π−) ............................... 95
5.7.1 TheEnsembleTestofhhDecays ............. 95
5.7.2 TheCorrelationCheck................... 98
5.7.3 ThecontinuumLRdistributionCheck. . . . . . . . . . . 99
5.7.4 The Calculation of Branching Fraction B . . . . . . . . . 100
6 Fitting Strategy and Result 103
6.1 ChargeAsymmetryACP ......................103
6.2 StrategyofFeedacross .......................104
6.3 FittingResult ............................106
6.4 BranchingFraction .........................110
6.4.1 ReconstructionEfficiency .................110
6.4.2 TheSummaryofBranchingFraction . . . . . . . . . . . 111
6.5 ChargeAsymmetryACP ......................112
7 Systematics and Efficiency Correction 115
7.1 LRcutsystematics .........................118
7.2 SystematicsonParticleIdentification . . . . . . . . . . . . . . . 119
8 Summary and Conclusion 121
A Figure of Merit 127
B Gsim Ensemble Test 133


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