臺灣博碩士論文加值系統

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
References 66

"Hou, Wei-Shu","Searching for the bottom counterparts of X(3872) and Y(4260) via pi+ pi- Upsilon","Phys.Rev. D"

"AlFiky, Mohammad T. and Gabbiani, Fabrizio and Petrov, Alexey A.","X(3872): Hadronic molecules in effective field theory","Phys.Lett. B"

"Ebert, D. and Faustov, R.N. and Galkin, V.O.","Masses of heavy tetraquarks in the relativistic quark model","Phys.Lett. B"

"Ebert, D. and Faustov, R.N. and Galkin, V.O.","Relativistic model of hidden bottom tetraquarks","Mod.Phys.Lett. A"

"Matheus, Ricardo D''Elia and Narison, S. and Nielsen, M. and Richard, J.M.","Can the X(3872) be a 1++ four-quark state?","Phys.Rev. D"

"Chatrchyan, Serguei and others","Measurement of the X(3872) production cross section via decays to J/psi pi pi in pp collisions at sqrt{s} = 7 TeV","ARXIV:1302.3968"

"Cronin-Hennessy, D. and others","Study of di-pion transitions among Upsilon(3S), Upsilon(2S), and Upsilon(1S) states","Phys.Rev. D"

"Tommaso Dorigo","Practical Calculations of the Look-Elsewhere Effect","http://www.pd.infn.it/~dorigo/LEE_example.ps"

"Acosta, D. and others","Observation of the Narrow State X(3872)→J/psipi+pi- in overline{p}p Collisions at sqrt{s}=1.96 TeV","Phys. Rev. Lett."

"Aaij, R. and others,"Determination of the X(3872) Meson Quantum Numbers","Phys. Rev. Lett."

"Choi, S.-K. and others","Observation of a Narrow Charmoniumlike State in Exclusive B+-→K+-pi+pi-J/psi Decays","Phys. Rev. Lett."

"Glen Cowan and Kyle Cranmer and Eilam Gross and Ofer Vitells","Asymptotic formulae for likelihood-based tests of new physics","Eur.Phys.J."

"Aubert, Bernard and others","Observation of a broad structure in the pi+pi-J/psi mass spectrum around 4.26 GeV/c2","Phys.Rev.Lett."

"Acosta, D. and others","Observation of the narrow state X(3872) to J/psi pi+pi- in pbar p collisions at sqrt{s} = 1.96 TeV","Phys.Rev.Lett."

"Abazov, V.M. and others","Observation and properties of the X(3872) decaying to J/psi pi+ pi- in pbar p collisions at sqrt{s} = 1.96 TeV}","Phys.Rev.Lett."

"Aubert, Bernard and others","Study of the B to J/psi K- pi+ pi- decay and measurement of the B to X(3872) K- branching fraction","Phys.Rev. D"

"Yuan, C.Z. and others","Measurement of e+e- to pi+pi- J/psi cross-section via initial state radiation at Belle","Phys.Rev.Lett."

"Aaij, R. and others","Observation of X(3872) production in pp collisions at sqrt{s}=7 TeV","Eur.Phys.J."

"CMS Collaboration","The CMS experiment at the CERN LHC","JINST"

"Sjostrand, Torbjorn and Mrenna, Stephen and Skands, Peter Z.","PYTHIA 6.4 Physics and Manual","JHEP"

"Lange, D.J.","The EvtGen particle decay simulation package","Nucl.Instrum.Meth."

"Agostinelli, S. and others","GEANT4: A simulation toolkit","Nucl.Instrum.Meth."

"Hoecker, Andreas and Speckmayer, Peter and Stelzer, Joerg and Therhaag, Jan and von Toerne, Eckhard and Voss, Helge","TMVA: Toolkit for Multivariate Data Analysis","PoS"

"Gross, Eilam and Vitells, Ofer","Trial factors or the look elsewhere effect in high energy physics","Eur.Phys.J."

"Read, Alexander L.","Presentation of search results: The CLs technique","J. Phys."