張寶棣臺灣大學:物理研究所雷永吉Lei, Yeong-JyiYeong-JyiLei2007-11-262018-06-282007-11-262018-06-282006http://ntur.lib.ntu.edu.tw//handle/246246/54486The CMS (Compact Muon Solenoid) experiment is located at the LHC (Large Hardon Collider) proton-proton collider in CERN. The center of mass energy of the proton-proton collider is 14 TeV. The experiment plans to start taking data at early 2008. Besides the pair top quark production observed by CDF (The Collider Detector at Fermilab) and D0 (DZero), the Standard Model also allows single top quark production which we expect to observe in the LHC with the CMS detector. The single top is produced by electroweak interaction and this gives us a window to directly measure the CKM (Cabbibo-Kobayashi-Maskawa) matrix element |Vtb| since the production cross section is proportional to jVtbj2. Assuming three quark generations or unitarity of the CKM matrix can imply |Vtb|~1. However, if the fourth generation exists, |Vtb| can be any number smaller then 1. There are three modes of single top production: (1) t-channel, (2) s-channel, and (3)W associated production or tW. Based on Monte Carlo simulation, a study of cross section and significance of tW production in the CMS experiment is presented in this thesis.Contents 1 Introduction 1 2 The LHC and the CMS Experiment 7 2.1 The Large Hadron Collider . . . . . . . . . . . . . . . . . . . . 7 2.2 CMS detector . . . . . . . . . . . . . . . . . . . . . . . . . . . 9 2.2.1 Magnet . . . . . . . . . . . . . . . . . . . . . . . . . . 9 2.2.2 Inner tracking system . . . . . . . . . . . . . . . . . . . 12 2.2.3 Electromagnetic calorimeter . . . . . . . . . . . . . . . 14 2.2.4 Hadron calorimeter . . . . . . . . . . . . . . . . . . . . 15 2.2.5 Muon chambers . . . . . . . . . . . . . . . . . . . . . . 16 2.2.6 The trigger system . . . . . . . . . . . . . . . . . . . . 17 3 Reconstruction 19 3.1 Track reconstruction . . . . . . . . . . . . . . . . . . . . . . . 19 3.2 Vertex reconstruction . . . . . . . . . . . . . . . . . . . . . . . 20 3.3 Muon reconstruction . . . . . . . . . . . . . . . . . . . . . . . 20 3.4 Electron reconstruction . . . . . . . . . . . . . . . . . . . . . . 21 3.5 Jet reconstruction . . . . . . . . . . . . . . . . . . . . . . . . . 21 3.6 b tagging . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22 5 6 CONTENTS 4 Simulation 27 4.1 Events generation . . . . . . . . . . . . . . . . . . . . . . . . . 27 4.2 Detector simulation . . . . . . . . . . . . . . . . . . . . . . . . 27 4.3 Adding pile-up events . . . . . . . . . . . . . . . . . . . . . . . 28 4.4 Digitization . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28 4.5 Fast Simulation . . . . . . . . . . . . . . . . . . . . . . . . . . 28 4.5.1 Pile-up treatments . . . . . . . . . . . . . . . . . . . . 28 4.5.2 Modification on FAMOS . . . . . . . . . . . . . . . . . 29 4.6 Event reconstruction . . . . . . . . . . . . . . . . . . . . . . . 29 5 Monte Carlo Samples 31 5.1 Backgrounds . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31 5.2 Monte Carlo production . . . . . . . . . . . . . . . . . . . . . 33 6 Extra Jet Reduction 35 6.1 Study with single muon sample . . . . . . . . . . . . . . . . . 35 6.2 Study with tW semi-leptonic sample . . . . . . . . . . . . . . 38 6.3 Pile-up jets reduction . . . . . . . . . . . . . . . . . . . . . . . 39 6.4 Extra jets reduction . . . . . . . . . . . . . . . . . . . . . . . . 42 7 Trigger and Event Selection 47 7.1 Triggers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 47 7.2 Lepton quality requirement . . . . . . . . . . . . . . . . . . . 48 7.3 Jet quality requirement . . . . . . . . . . . . . . . . . . . . . . 49 7.4 b tagging . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 49 7.5 Isolation cuts . . . . . . . . . . . . . . . . . . . . . . . . . . . 49 7.6 Kinematic cuts . . . . . . . . . . . . . . . . . . . . . . . . . . 50 CONTENTS 7 7.7 Event reconstruction . . . . . . . . . . . . . . . . . . . . . . . 50 7.7.1 The hadronic decayed W . . . . . . . . . . . . . . . . . 50 7.7.2 The leptonic decayed W . . . . . . . . . . . . . . . . . 51 7.7.3 The top quark reconstruction . . . . . . . . . . . . . . 52 7.8 The signal region . . . . . . . . . . . . . . . . . . . . . . . . . 53 7.9 Estimation of efficiencies . . . . . . . . . . . . . . . . . . . . . 53 7.10 Summary of efficiencies and expected yields . . . . . . . . . . 57 8 Cross Section Measurement 59 8.1 Cross section and uncertainty . . . . . . . . . . . . . . . . . . 59 8.2 The ratio method . . . . . . . . . . . . . . . . . . . . . . . . . 60 8.3 Uncertainty with ratio method . . . . . . . . . . . . . . . . . . 61 8.4 The background box . . . . . . . . . . . . . . . . . . . . . . . 62 9 Systematic Uncertainties 63 9.1 Luminosity . . . . . . . . . . . . . . . . . . . . . . . . . . . . 64 9.2 Theoretical cross section . . . . . . . . . . . . . . . . . . . . . 64 9.3 Jet energy scale . . . . . . . . . . . . . . . . . . . . . . . . . . 65 9.4 B tagging efficiency . . . . . . . . . . . . . . . . . . . . . . . . 65 9.5 Parton Distribution Functions . . . . . . . . . . . . . . . . . . 65 9.6 Amount of pile-up events . . . . . . . . . . . . . . . . . . . . . 67 9.7 Monte Carlo statistics . . . . . . . . . . . . . . . . . . . . . . 67 9.8 Summary of systematic uncertainty . . . . . . . . . . . . . . . 67 10 Significance 69 10.1 Significance estimators . . . . . . . . . . . . . . . . . . . . . . 69 10.2 Estimation of ¢B . . . . . . . . . . . . . . . . . . . . . . . . . 70 8 CONTENTS 10.3 Calculation of the significance . . . . . . . . . . . . . . . . . . 71 11 Conclusion 751446395 bytesapplication/pdfen-US夸克單夸克單一夸克topquarksingle topLHCCMS尋找與W玻色子共同產生之單一頂夸克Search of W-associated Production of Single Top Quarks in CMSthesishttp://ntur.lib.ntu.edu.tw/bitstream/246246/54486/1/ntu-95-R93222005-1.pdf