本論文試圖於
Υ(1S)→μ+μ-π+π−衰變途徑中，尋找奇特魅夸克共振態X(3872)的底夸克對應共振態(Xb)。經由分析在質心能量8 TeV條件下，累計亮度20.65/fb的質子--質子對撞事件，在掃描的能量區間10-11 GeV/c^2內並未顯示出任何Xb的存在線索，對應的區域顯著性為2.6個標準差，全域顯著性為0.8個標準差。在95%信心水準下，可以給出在此特定衰變途徑下相對於Υ(2S)的散射截面比值上限為0.8--4.6%(隨Xb的靜止質量變動)。

We report a search for a bottomonium counterpart of exotic charmonium state X(3872), denoted as Xb throughout this thesis. The target decay channel is Xb→Υ(1S)π+π−→μ+μ-π+π−. An integrated luminosity of 20.65/fb at proton-proton collision at sqrt{s}=8 TeV is analyzed. In the search phase space, |y_{Xb}| < 2.0, p_{T,Xb} > 13.5 GeV/c^2, and 10 < M_{Xb} < 11 GeV/c^2, the maximum local significance is 2.6 sigma, which equals to 0.8 sigma global significance. The upper limit at 95% confidence level is settled to be 0.8-4.6% (depend on the mass of Xb) as the cross section of Υ(1S)→Υ(1S)π+π−.

Contents
1 Introduction 1
2 Data and Simulation Samples 4
3 Trigger and Event Selection 7
3.1 Selection Optimization . . . . . . . . . . . . . . . . . . . . . . . . . 11
3.2 Simulation Validation . . . . . . . . . . . . . . . . . . . . . . . . . . 20
4 Limit Calculation 23
4.1 Observed data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24
4.2 Signal modeling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24
4.3 Background modeling . . . . . . . . . . . . . . . . . . . . . . . . . . 28
4.4 Calculation of p-value and limit . . . . . . . . . . . . . . . . . . . 32
4.5 Look-elsewhere E ffect . . . . . . . . . . . . . . . . . . . . . . . . . . 36
5 Systematic Uncertainties 38
5.1 Signal decay model . . . . . . . . . . . . . . . . . . . . . . . . . . . 38
5.2 Υ(1S) polarization . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39
5.3 Signal resolution . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40
5.4 Signal lineshape modeling . . . . . . . . . . . . . . . . . . . . . . . 41
5.5 Reconstruction effi ciency modeling . . . . . . . . . . . . . . . . . . 42
5.6 Background modeling . . . . . . . . . . . . . . . . . . . . . . . . . . 43
5.7 Result with systematic uncertainties . . . . . . . . . . . . . . . . 44
6 Summary 49
A Experiment Setup 50
A.1 The Large Hadron Collider . . . . . . . . . . . . . . . . . . . . . . 50
A.2 The Compact Muon Solenoid detector . . . . . . . . . . . . . . . 55
A.2.1 Magnet . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 57
A.2.2 Tracking system . . . . . . . . . . . . . . . . . . . . . . . . 58
A.2.3 Electromagnetic calorimeter . . . . . . . . . . . . . . . . . 60
A.2.4 Hardron calorimeter . . . . . . . . . . . . . . . . . . . . . . 61
A.2.5 Muon system . . . . . . . . . . . . . . . . . . . . . . . . . . 62
B Physical Object Reconstruction 64
B.1 Track . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 64
B.2 Muon . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 64
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