雙光子反應產生KsKs的研究｜國立中央大學博碩士論文系統

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研究生：	陳婉婷 Wan-Ting Chen
論文名稱：	雙光子反應產生KsKs的研究 A study of γγ → KS0 KS0 production atenergies of 2.4 - 4.0 GeV at Belle
指導教授：	陳鎰鋒 A.E. Chen
口試委員:
學位類別：	博士 Doctor
系所名稱：	理學院 - 物理學系 Department of Physics
畢業學年度：	95
語文別：	英文
論文頁數：	106
中文關鍵詞：	雙光子、量子色動力學
外文關鍵詞：	pQCD, two-photon, charmonium
相關次數：	點閱：5 下載：0
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本論文測量雙光子反應γγ→KS0 KS0 反應的截面積，其中雙光子質心能量介於2.4GeV 至4.0GeV，Ks 的散射角θ*在|cosθ*|<0.6 範圍之內。本論文數據來自位於日本筑波市文部省高能物理加速器研究機構內之正負電子對撞機產生之雙光子事件，其總亮度為397.6fb-1。
本論文利用Monte-Carlo 事件模擬找出挑選KS0 的最佳分析方法，並減去背景事件所佔的比率，得到精確的截面積與角度分佈結果。本實驗結果得到在雙光子質心能量介於2.4GeV 至4.0GeV 之間，其截面積與不變質量的-10.5±0.6±0.4 次方成正比，此為目前能量不適合驗
證微擾量子色動力學對粒子生成機制描述的理論（包括handbag 模型與雙夸克對模型）之證據。但是從與γγ→K+K-截面積比較後，發現其比值下降之趨勢完全無法由handbag 模型解釋，所以可得知不管是目前的能量或是更高的能量，handbag 模型的貢獻完全不需要被考慮。本論文成功排除handbag 模型的貢獻。
在γγ→KS0 KS0 反應我們亦觀測到χc0 和χc2 的訊號。其雙光子寬度與衰變至KS0 KS0 的乘積為
Γγγ(χc0)B(χc0→KsKs)=7.00±0.65±0.66 eV
Γγγ(χc2)B(χc2→KsKs)=0.31±0.05±0.03 eV

K0S K0S production in two-photon collisions is measured using data corresponding to 397.6 fb−1 integrated luminosity collected with the BELLE detector at the KEKB e+e− collider. The cross section and angular distribution are measured in the two-photon center-of-mass energy (W) range between 2.4 GeV< W <4.0 GeV and | cos θ∗| < 0.6. A sin−4 θ∗ behavior of the cross section in 2.4 GeV< W <4.0 GeV is observed. Signals of χc0 and χc2 are also observed.

Theory 1
1 Introduction . 1
2 The kinematics of two-photon reaction . 2
3 The helicity structure of the two-photon cross section . 3
4 Luminosity function . 6
5 Theoretical Prediction for γγ → MM Processes . 7
5.1 Leading term QCD . 7
5.2 Handbag Model . 12
5.3 Summary . 16
Experimental Apparatus 17
1 Requirements of the detectors to measure two-photon reactions . 17
2 The KEKB collider . 18
3 The Belle detector . 20
3.1 Beam pipe . 20
3.2 Silicon Vertex Detector (SVD) . 21
3.3 Central Drift Chamber (CDC) . 22
3.4 Aerogel ˇCerenkov counters (ACC) . 25
3.5 Time of Flight (TOF) . 28
3.6 Electromagnetic Calorimeter (ECL) . 29
3.7 Extreme Forward Calorimeter (EFC) . 31
3.8 Solenoid Magnet . 32
3.9 KL and muon detector (KLM) . 33
3.10 Trigger . 33
3.11 Data Acquisition (DAQ) . 39
3.12 Offline Computing System . 40
Analysis for γγ → K0S K0S cross section measurements 43
1 Event selection . 43
1.1 K0S identification . 44
2 Monte Carlo simulation . 46
2.1 Two-photonic REsonance Production Simulator (TREPS) . 48
2.2 Detection efficiency . 49
2.3 Trigger efficiencies . 49
3 Background study . 49
3.1 Two-photon four-charged events . 51
3.2 Non-exclusive events . 52
4 Systematic errors . 54
4.1 K0S particle identification . 54
4.2 Luminosity function . 56
4.3 Trigger efficiency . 56
4.4 Summary of systematic uncertainties . 57
Results and Discussion 59
1 Results . 59
2 Discussion . 59
2.1 W-dependence . 59
2.2 Angular dependence . 62
2.3 Transition of the ratio of σ0(γγ → K0S
K0S )/σ0(γγ → K+K−) . 62
χc0 and χc2 measurements 65
1 The estimation of yields . 65
2 Derivation of cross section, two-photon decay widths and branching fractions 67
3 Comparison with the results of γγ → K+K− and γγ → π+π− of Belle . 70
4 Comparison with other experiments . 71
5 Angular distribution of χcJ . 72
Conclusion 75
A Selection rules for γγ → X process 81
A.1 Selection rules for the dematerialization of two photons into a particle . 81
A.2 Angular distribution of γγ → χc2 . 82
B Likelihood Fitting 85
C Estimation of charmonium events dominated by ISR events 87

                                

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