臺灣博碩士論文加值系統

我們在位於日本大強度質子加速器研究綜合機構(J-Parc)的KOTO實驗中尋找長生命期中性K介子(KL)的電荷宇稱不守恆衰變KL→π0νν ̄。在標準模型中此衰變模式的分支比有明確的計算結果,且其預測值僅:Br(KL→π0νν ̄)=(3.00±0.30)×10−11。基於此特性,測量KL→π0νν ̄的分支比不僅可以直接測量CKM矩陣中的參數η,更是一個有機會發現新物理的良好途徑。
本論文使用KOTO實驗於西元2015年取得的數據,其數據量約莫2013年5月的20倍。2015年的數據依照月份及其質子束通量可分為9個時期,我們首先利用衰變模式KL→3π0、KL→2π0以及KL→γγ分別對每個時期的數據做KL於KOTO偵測器前方的通量分析,不同衰變模式的結果在系統誤差的估計範圍內。
在KL→π0νν ̄分析中,我們使用盲測實驗法,並且以得到的通量作為歸一化常數,分析可能的背景事件、系統誤差以及計算對單一訊號事件敏感度(S.E.S.)。該分析的結果為
S.E.S.=(1.27±0.01stat±0.1sys)×10−9
其預期的背景事件數量為1.32±0.33。除此之外,在尋找KL→π0X,(X→不可見粒子)衰變的分析中,我們利用KL→π0νν ̄的蒙地卡羅模擬計算出不同X質量對應到的對單一訊號事件敏感度,得到當X質量等於π0質量時,其對單一訊號事件敏感度為0.99×10−9。

A search of a direct CP-violating decay K L → π 0 ν ν ̄ is performedin KOTO experiment, which was launched in Japan Proton AcceleratorComplex (J-Parc). K L → π 0 ν ν ̄ is highly suppressed in the Standard Model (SM), and the branch ratio Br(K L → π 0 ν ν ̄ ) = (3.00 ± 0.30) ×10 −11 is given by the SM prediction. Due to its theoretically cleanness, the measurement of K L → π 0 ν ν ̄ branching ratio provide a direct measurement of η in CKM matrix, as well as a good probe to the New Physics.
This thesis performs an analysis with data collected in 2015, in which the statistics of data is about 20 times larger than that taken in May 2013. There are 9 periods with different intensity of K L beam during the 4-months data taking in 2015. The analysis of K L flux has been done for each periods using 3 normalization modes: K L → 3π 0 , K L → 2π 0 , and K L → γγ, and the results are consistent with each other.
Using the blind analysis method, a search for K L → π 0 ν ν ̄ , which consists of estimation of systematic uncertainty, background study, and normalization, is then performed based on 2015 data. As a preliminary result, the single event sensitivity (S.E.S.) is obtained as
S.E.S. = (1.27 ± 0.01 stat ± 0.1 sys ) × 10 −9 .
The expected number of background in the signal region is 1.32±0.33. In addition, for K L → π 0 X, (X → invisible) search, X mass is calculated by means of invariant mass of ν ν ̄ in K L → π 0 ν ν ̄ MC simulation, and S.E.S. for M X = M π 0 is obtained as 0.99 × 10 −9 .

Acknowledgements . . . . . . . . . . . . . . . . . . . . v
摘要. . . . . . . . . . . . . . . . . . . . vii
Abstract . . . . . . . . . . . . . . . . . . . . ix
1 Introduction . . . . . . . . . . . . . . . . . . . . 1
1.1 Motivation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
1.2 Standard Model and CKM Matrix . . . . . . . . . . . . . . . . . . . 1
1.3 CP-violation in Neutral Kaon System . . . . . . . . . . . . . . . . . 3
1.4 KL ! 0 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
1.5 Beyond Standard Model . . . . . . . . . . . . . . . . . . . . . . . . . 6
2 The KOTO Experiment 7
2.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
2.2 Strategy to Detect KL ! 0 . . . . . . . . . . . . . . . . . . . . . 7
2.3 KOTO Beam Line . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
2.3.1 Primary Proton Beam Line . . . . . . . . . . . . . . . . . . . 8
2.3.2 KL Beam Line . . . . . . . . . . . . . . . . . . . . . . . . . . 9
2.4 CsI Calorimeter . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
2.5 Hermetic Veto Detectors . . . . . . . . . . . . . . . . . . . . . . . . . 11
2.5.1 Barrel Photon Veto . . . . . . . . . . . . . . . . . . . . . . . . 11
2.5.2 Barrel Charged Veto . . . . . . . . . . . . . . . . . . . . . . . 12
2.5.3 Charged Veto . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
2.5.4 Neutron Collar Counter and HINEMOS . . . . . . . . . . . . 14
2.5.5 Veto Detectors Near The CsI Calorimeter . . . . . . . . . . . 15
2.5.6 Collar Counters at CSI Downstream and Beam Pipe Charge
Veto . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15
2.5.7 Charged Veto and Photon Veto at Beam Hole . . . . . . . . . 16
2.6 Data Acquisition System . . . . . . . . . . . . . . . . . . . . . . . . . 18
2.6.1 ADC system . . . . . . . . . . . . . . . . . . . . . . . . . . . 19
2.6.2 Trigger system . . . . . . . . . . . . . . . . . . . . . . . . . . 20
3 Data Taking and Detector Calibration 23
3.1 Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23
3.2 Accelerator Condition . . . . . . . . . . . . . . . . . . . . . . . . . . 23
3.3 Trigger Condition . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24
3.3.1 Minimum Bias Trigger . . . . . . . . . . . . . . . . . . . . . . 24
3.3.2 Normalization Trigger . . . . . . . . . . . . . . . . . . . . . . 24
3.3.3 Physics Trigger . . . . . . . . . . . . . . . . . . . . . . . . . . 24
3.3.4 Calibration Trigger . . . . . . . . . . . . . . . . . . . . . . . . 25
3.3.5 Off-spill Cosmic Ray Trigger . . . . . . . . . . . . . . . . . . . 25
3.3.6 External Triggers . . . . . . . . . . . . . . . . . . . . . . . . . 26
3.4 Special Runs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27
3.4.1 Aluminium Target Runs . . . . . . . . . . . . . . . . . . . . . 27
3.4.2 TMon Run . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27
3.4.3 Beam Muon Run . . . . . . . . . . . . . . . . . . . . . . . . . 28
3.4.4 Cosmic Ray Run . . . . . . . . . . . . . . . . . . . . . . . . . 28
3.5 DAQ performance and Accumulation of Physics data . . . . . . . . . 29
3.6 Detector Calibration . . . . . . . . . . . . . . . . . . . . . . . . . . . 31
3.6.1 Energy Calibration and Timing Calibration of CsI . . . . . . 31
3.6.2 Energy Calibration and Timing Calibration of Veto Detectors 35
4 Monte Carlo Simulation 37
4.1 Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37
4.2 KL Generation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37
4.2.1 KL Momentum Spectrum . . . . . . . . . . . . . . . . . . . . 37
4.2.2 KL Incident Position and Direction . . . . . . . . . . . . . . . 38
4.2.3 KL Decay and Particle Interaction with Material . . . . . . . 39
4.3 Detector Response . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40
4.3.1 CsI . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40
4.3.2 CBAR and BCV . . . . . . . . . . . . . . . . . . . . . . . . . 41
4.3.3 CV . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42
4.3.4 Other Detectors . . . . . . . . . . . . . . . . . . . . . . . . . 44
4.4 Waveform Simulation . . . . . . . . . . . . . . . . . . . . . . . . . . . 44
4.5 Reproduction of Pileup and Noise . . . . . . . . . . . . . . . . . . . . 45
4.6 Fast Simulation and Recycling . . . . . . . . . . . . . . . . . . . . . . 46
4.7 Simulation of Non-KL Decaying backgrounds . . . . . . . . . . . . . 46
5 Event Reconstruction 49
5.1 Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 49
5.2 Photon Cluster Finding . . . . . . . . . . . . . . . . . . . . . . . . . 49
5.3 0 Reconstruction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 51
5.4 KL Reconstruction from KL ! 3 0, KL ! 2 0, KL ! . . . . . . 52
5.5 Correction of Photon Hit Position and Shower Leakage . . . . . . . . 54
5.6 Reconstruction of Veto Information . . . . . . . . . . . . . . . . . . . 55
5.6.1 Veto conditions . . . . . . . . . . . . . . . . . . . . . . . . . . 55
5.6.2 Reconstruction of Veto Energy and Veto Timing . . . . . . . 55
6 KL Flux Study . . . . . . . . . . . . . . . . . . . . 61
6.1 Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 61
6.2 Veto Cuts and Event Selections . . . . . . . . . . . . . . . . . . . . . 61
6.2.1 Veto Cuts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 61
6.2.2 Photon Selections . . . . . . . . . . . . . . . . . . . . . . . . . 62
6.2.3 KL Selections for KL ! 3 0 . . . . . . . . . . . . . . . . . . . 63
6.2.4 KL Selection for KL ! 2 0 . . . . . . . . . . . . . . . . . . . 64
6.2.5 KL Selections for KL ! . . . . . . . . . . . . . . . . . . . 65
6.3 Data Sets and MC Simulation Samples . . . . . . . . . . . . . . . . . 66
6.4 Flux Calculation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 66
6.4.1 KL ! 3 0 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 67
6.4.2 KL ! 2 0 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 71
6.4.3 KL !

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 74
6.5 Estimation of Systematic Uncertainties . . . . . . . . . . . . . . . . . 81
6.6 Combination of Three Modes . . . . . . . . . . . . . . . . . . . . . . 84
6.7 Discussion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 85
6.7.1 Data Checking and KL Flux Stability . . . . . . . . . . . . . 85
6.8 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 87
7 KL ! 0 Analysis 91
7.1 Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 91
7.2 Event selection for KL ! 0 . . . . . . . . . . . . . . . . . . . . . 91
7.2.1 Photon Selections . . . . . . . . . . . . . . . . . . . . . . . . . 91
7.2.2 KL Decaying Background Rejection . . . . . . . . . . . . . . . 92
7.2.3 Neutron Background Suppression . . . . . . . . . . . . . . . . 93
7.2.4 Veto Cuts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 97
7.2.5 Blinding the Signal Region . . . . . . . . . . . . . . . . . . . 98
7.3 Determination of Normalization Factor . . . . . . . . . . . . . . . . . 100
7.4 Systematic Uncertainty . . . . . . . . . . . . . . . . . . . . . . . . . . 105
7.5 Background Estimation . . . . . . . . . . . . . . . . . . . . . . . . . 110
7.5.1 KL ! 2 0 Background . . . . . . . . . . . . . . . . . . . . . . 111
7.5.2 KL → +

[1] Andrei D. Sakharov. Special issue: Violation of CP in variance, C asymmetry,and baryon asymmetry of the universe. Soviet Physics Uspekhi, 34:392–393,may 1991.
[2] Makoto Kobayashi and Toshihide Maskawa. Cp violation in the renormalizabletheory of weak interaction. Prog. Theor. Phys., 49:652–657, 1973.
[3] Nicola Cabibbo. Unitary symmetry and leptonic decays. Phys. Rev. Lett.,10:531–533, Jun 1963.
[4] Lincoln Wolfenstein. Parametrization of the kobayashi-maskawa matrix. Phys.Rev. Lett., 51:1945–1947, Nov 1983.
[5] K. Anikeev et al. b physics at the tevatron: Run ii and beyond. In Workshopon B Physics at the Tevatron: Run II and Beyond Batavia, Illinois, September23-25, 1999, 2001.
[6] Patrick Koppenburg and Sebastien Descotes-Genon. The CKM parameters.2017.
[7] J. H. Christenson, J. W. Cronin, V. L. Fitch, and R. Turlay. Evidence for the2 decay of the k20 meson. Physical Review Letters, 13:138–140, July 1964.
[8] Mark Thomson. Modern particle physics. Cambridge University Press, NewYork, 2013.
[9] K. A. Olive et al. Review of Particle Physics. Chin. Phys., C38:090001, 2014.
[10] Gerhard Buchalla and Andrzej J. Buras. The rare decays K ! , B ! x and B ! l+l