臺灣博碩士論文加值系統

We study the baryonic charmonium decays of B mesons, B+ to etac K+ and B+ to J/psi K+, where the etac and J/psi subsequently decay into a p pbar or Lambda Lambdabar pair. We measure the J/psi to p pbar, Lambda Lambdabar anisotropy parameters, alpha_B = -0.60 +- 0.13 +-0.14 (p pbar), -0.44 +- 0.51 +- 0.31 (Lambda Lambdabar) and compare to results from e+e- to J/psi formation experiments. We also report the first observation of etac to Lambda Lambdabar. The measured branching fraction is B(etac to Lambda Lambdabar) = (0.87 +0.24 -0.21(stat) +0.09 -0.14(syst) +- 0.27 (PDG)) x 10^-3. This study is based on a 357 fb^-1 data sample recorded on the Upsilon(4S) resonance with the Belle detector at the KEKB asymmetric-energy e+e- collider.

1 Introduction
1.1 The Standard Model . . . . . . . . . . . . . . . . . . . . . . . 1
1.1.1 Fundamental particles . . . . . . . . . . . . . . . . . . 1
1.1.2 The CKM matrix . . . . . . . . . . . . . . . . . . . . . 3
1.2 B mesons . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
1.3 Etac and J/psi mesons . . . . . . . . . . . . . . . . . . . . . . . . 4
1.4 J/psi and etac decay into baryon-antibaryon pairs . . . . . . . . 6
1.5 Thesis outline . . . . . . . . . . . . . . . . . . . . . . . . . . . 7

2 Analysis Method
2.1 B candidate selection . . . . . . . . . . . . . . . . . . . . . . . 8
2.2 Background Suppression technique . . . . . . . . . . . . . . . 10
2.2.1 Super Fox-Wolfram Moments . . . . . . . . . . . . . . 10
2.2.2 Cos_thetathrust and Spher . . . . . . . . . . . . . . . . . . . . 11
2.2.3 Fisher discrimination . . . . . . . . . . . . . . . . . . . 12
2.2.4 Information from Upsilon(4S) decay . . . . . . . . . . . . . . 12
2.3 Likelihood Ratio . . . . . . . . . . . . . . . . . . . . . . . . . 14
2.3.1 Definition . . . . . . . . . . . . . . . . . . . . . . . . . 14
2.3.2 Optimization of likelihood ratio cut . . . . . . . . . . . 14
2.4 Chisq2 and likelihood fits . . . . . . . . . . . . . . . . . . . . . . . 15
2.5 Branching fraction determination . . . . . . . . . . . . . . . . 16
2.5.1 Systematic error study . . . . . . . . . . . . . . . . . . 16

3 J/psi decays into baryon-antibaryon pairs angular distributions
18
3.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18
3.2 Particle Selection . . . . . . . . . . . . . . . . . . . . . . . . . 19
3.2.1 Proton and Kaon selection . . . . . . . . . . . . . . . . 19
3.2.2 Good ¤ reconstruction . . . . . . . . . . . . . . . . . . 20
3.2.3 B reconstruction . . . . . . . . . . . . . . . . . . . . . 20
3.3 Data sample . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22
3.4 Background suppression . . . . . . . . . . . . . . . . . . . . . 22
3.5 Invariant mass spectra and Dalitz plots . . . . . . . . . . . . . 23
3.5.1 Mpp and MLL spectra . . . . . . . . . . . . . . . . . . . 23
3.5.2 Dalitz plots . . . . . . . . . . . . . . . . . . . . . . . . 23
3.6 J/psi decay angle distributions . . . . . . . . . . . . . . . . . . 25
3.6.1 Previous measurements . . . . . . . . . . . . . . . . . . 25
3.6.2 J/psi to ppbar . . . . . . . . . . . . . . . . . . . . . . . . . 25
3.6.3 J/psi to Lambda Lambdabar . . . . . . . . . . . . . . . . . . . . . . . . . 27
3.6.4 Toy Monte Carlo study . . . . . . . . . . . . . . . . . . 27
3.6.5 Efficiency study . . . . . . . . . . . . . . . . . . . . . . 27
3.6.6 Check on ´c and Kaon decay angle distribtuion . . . . 28
3.7 Systematic uncertainty . . . . . . . . . . . . . . . . . . . . . . 34
3.8 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35

4 Observation of etac to Lambda Lambdabar ……36
4.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36
4.2 selection . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37
4.3 Physics result . . . . . . . . . . . . . . . . . . . . . . . . . . . 38
4.3. Etac to Lambda Lambdabar branching fraction . . . . . . . . . . . . . . . 38
4.3.Etac width . . . . . . . . . . . . . . . . . . . . . . . . . . 39
4.3.3 Branching fractions of charmonium decays into baryonantibaryon
pairs . . . . . . . . . . . . . . . . . . . . . . 40
4.4 Systematic uncertainty . . . . . . . . . . . . . . . . . . . . . . 42
4.5 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43
5 Conclusions and Prospects 45
5.1 J/psi decay angle distributions . . . . . . . . . . . . . . . . . . 45
5.2 Observation of etac to Lambda Lambdabar . . . . . . . . . . . . . . . . . . . . . 46
5.3 Direct CP violation in B to ppbar, Lambda Lambdabar . . . . 47

A Search for B to K* nu nubar 48
A.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . 48
A.2 Data sample . . . . . . . . . . . . . . . . . . . . . . . . . . . . 49
A.3 Event selection . . . . . . . . . . . . . . . . . . . . . . . . . . 50
A.4 Estimation of signal and background . . . . . . . . . . . . . . 51
A.5 Control Sample . . . . . . . . . . . . . . . . . . . . . . . . . . 56
A.6 Systematic uncertainties . . . . . . . . . . . . . . . . . . . . . 58
A.7 Result . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 60
A.8 Result of tight cut . . . . . . . . . . . . . . . . . . . . . . . . 64
A.9 Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . 69
A.10 Event display . . . . . . . . . . . . . . . . . . . . . . . . . . . 70
A.10.1 ExpNo. 7, RunNo. 895, EvtNo. 1296067 . . . . . . . . 70
A.10.2 ExpNo. 41, RunNo. 1019, EvtNo. 6328924 . . . . . . . 70
A.10.3 ExpNo. 43, RunNo. 4, EvtNo. 3870356 . . . . . . . . . 71
A.10.4 ExpNo. 43, RunNo 424., EvtNo. 4803757 (K* gamma candidate)
. . . . . . . . . . . . . . . . . . . . . . . . . . . . 71

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