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Production of J/ψ in p+p collisions at √s = 7 TeV in CMS

초록/요약

The production of J/ψ has been thought as an interesting physics topic in both proton-(anti)proton and heavy-ion collisions. Since not only J/ψ production mechanism is ideal testing ground of QCD but also suppression of J/ψ yield in heavy-ion collisions comparing to that of p+p collisions is one of the good signals to probe Quark-Gluon Plasma. In this thesis, studies of CMS muon trigger as a preparation for the 2010 LHC startup run and measurements of J/ψ production using the data collected by the CMS detector in the first p+p collisions at √s = 7 TeV are presented. Making use of the large B-hadron lifetime, non-promptly produced J/ψ's from B-hadron decays are separate from the prompt J/ψ's. Eventually, inclusive and prompt J/ψ differential cross section, as a function of the J/ψ transverse momentum, obtained from the early p+p runs of corresponding integrated luminosity 2.86 pb-1 will be shown at the end.

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목차

1 Introduction 1
2 Theoretical overview 4
2.1 Charmonium family . . . . . . . . . . . . . . . . . . . . . . . . 5
2.2 Charmonium Production . . . . . . . . . . . . . . . . . . . . . 6
2.2.1 Color Singlet Model . . . . . . . . . . . . . . . . . . . 9
2.2.2 NRQCD approach and Color Octet Model . . . . . . . 11
2.2.3 Color Evaporation Model . . . . . . . . . . . . . . . . . 14
2.2.4 J/ψ from B-hadron decay . . . . . . . . . . . . . . . . 14
2.3 Charmonium measurements at hadron colliders . . . . . . . . 16
2.3.1 Charmonium at Tevatron . . . . . . . . . . . . . . . . 16
2.3.2 Charmonium at SPS and RHIC . . . . . . . . . . . . . 21
3 LHC and CMS experiment 29
3.1 Large Hadron Collider at CERN . . . . . . . . . . . . . . . . . 29
3.1.1 Physics at LHC . . . . . . . . . . . . . . . . . . . . . . 32
3.1.2 The LHC Startup Condition . . . . . . . . . . . . . . . 37
3.2 Compact Muon Solenoid Detector . . . . . . . . . . . . . . . . 39
3.2.1 Magnet . . . . . . . . . . . . . . . . . . . . . . . . . . 41
3.2.2 Inner Tracker . . . . . . . . . . . . . . . . . . . . . . . 42
3.2.3 Electromagnetic Calorimeter . . . . . . . . . . . . . . . 44
3.2.4 Hadron Calorimeter . . . . . . . . . . . . . . . . . . . . 47
3.2.5 Muon System . . . . . . . . . . . . . . . . . . . . . . . 48
3.2.6 Trigger and data acquisition . . . . . . . . . . . . . . . 51
4 CMS Muon trigger system and J/ψ trigger 56
4.1 CMS Muon trigger system . . . . . . . . . . . . . . . . . . . . 56
4.1.1 Muon Level-1 Trigger . . . . . . . . . . . . . . . . . . . 56
4.1.2 Muon HLT . . . . . . . . . . . . . . . . . . . . . . . . 57
4.2 Feasibility study of low pT dimuon trigger for J/ψ . . . . . . . 59
4.2.1 Dimuon triggering strategy for heavy-ion collisions . . . .59
4.2.2 Rate estimation by low-pT dimuon trigger in p+p collisions 63
4.3 An improvement of J/ψ trigger for early CMS p+p data . . . 66
4.3.1 Description of Muon+Track triggers . . . . . . . . . . . 66
4.3.2 Trigger rates and efficiency . . . . . . . . . . . . . . . 67
5 Monte-Carlo and Data samples 71
5.1 Monte-Carlo samples . . . . . . . . . . . . . . . . . . . . . . . 71
5.2 Datasets . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 72
6 Data and J/ψ selection 74
6.1 Data selection . . . . . . . . . . . . . . . . . . . . . . . . . . . 74
6.2 Offine muon reconstruction . . . . . . . . . . . . . . . . . . . 75
6.3 J/ψ selection . . . . . . . . . . . . . . . . . . . . . . . . . . . 77
7 Measurement of inclusive and prompt J/ψ cross-section 79
7.1 Acceptance of J/ψ . . . . . . . . . . . . . . . . . . . . . . . . 80
7.2 Muon Effciencies by Tag and Probe Method . . . . . . . . 82
7.2.1 Tag and Probe Method . . . . . . . . . . . . . . . . . . 84
7.2.2 Tracking Effciency by T&P . . . . . . . . . . . . . . . 85
7.2.3 Muon Identification Effciency by T&P . . . . . . . . . 88
7.2.4 Trigger Effciency by T&P . . . . . . . . . . . . . . . . 92
7.2.5 Track quality efficiency . . . . . . . . . . . . . . . . . . 96
7.2.6 Muon correlations . . . . . . . . . . . . . . . . . . . . . 96
7.3 Inclusive J/ψ Cross-section . . . . . . . . . . . . . . . . . . . 96
7.3.1 Systematic Uncertainties of inclusive J/ψ cross section 102
7.4 Fraction of J/ψ from B-hadron decay and prompt J/ψ cros ssection. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 103
7.4.1 Comparison with models . . . . . . . . . . . . . . . . . 108
8 Conclusions 114

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