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42 The Data Sample and Object Identification As Photons are not used to re any trigger, only the p T > 15 GeV threshold is required. The isolation requirement is maintained to reduce QCD-contamination: π are major components of a hadron jet; their decay into a pair of gammas produces EM-candidates, 0 most of them unisolated. This analysis focuses on isolated photons from non-SM particle decays like X ′ → γ + X. With the help of isolation they can be separate properly from the QCD-background and from low-p T initial or nal state radiation (see Section 5.1). 4.3.3 Muon Candidates Muons are reconstructed using information from two independent detector systems: the muon detector with its scintillators and drift tubes, and the central tracker. A local track in the Muon System is the basis of muon identication; an associated central track provides precise p T measurement. The analysis presented here considers only high quality muons with a local track and a correlated central track in order to combine the superior track resolution of the tracker with the clear object identication of the Muon System (only muons traverse the calorimeter). The potentially problematic background of misreconstructed muons and cosmics is therefore minimized. Muons are selected combining the certied muon object denitions by the Muon-ID Group [34] with additional quality cuts, special terms will be explained further below: • nseg = 3 muon with medium quality • standard timing cut against cosmics • central track with N SMT ≥ 3 • χ 2 track /dof < 3.5 for central track t < 160 for global t between track and muon system • χ 2 global • track origins from assumed primary vertex: |z track − z vertex | < 2 cm • isolation criteria • muon with p T > 15 GeV • detector-|η| < 1.4 A nseg = 3 muon is required to have a central track matched to muon segments. The local track must include hits before and after the toroid (A and BC layer). These hits are tted toformalocaltrack. Thelocaltrackisprobablybetterdesignatedatrackcandidate asa specic quality of the track t is not required in nseg = 3. This track is then extrapolated to the tracker to match with a central track. If the t of the local track does not converge, the matching is done starting from the tracker and extrapolating to the muon system. One of these overall ts must converge, but the local track itself can be poorly reconstructed. In principle both tracks can now be combined into a global track to give the 4-vector of the muon, its charge, η, ϕ and the z-coordinate. Unfortunately this global track is not well understood, and kinematic variables measured only by the central track are more reliable. As a consequence, the local muon system is used only to provide object identication by
4.3. Object Identification and Selection Cuts 43 matching the central track to the hits in the muon system. The quality medium in combination with a certain nseg-value determines the number of wireandscintillatorhits: AtleasttwoAlayerwirehits, atleastoneAlayerscintillatorhit, at least two BC layer wire hits, and at least one BC scintillator hit. With hits before and after the toroid a local track can be dened more easily, and the requirement of numerous wire and scintillator hits minimizes noise eects. The standard loose cut against cosmics is applied based on timing information from scintillatorhits. Torejectcosmicraymuons, thetransittimeinscintillatorlayersA, t A , andin scintillatorlayersBC, t BC , mustbeconsistentwiththetime-of-ightformuonsoriginating from a beam collision: |t A | < 10ns and −15ns < t BC < 10ns As a C-layer scintillation counter achieves a timing resolution of 2.5 ns, this cut ensures that the muons studied emerge from the hard scatter process and are not of cosmic origin. In the nal sample (i.e. all cuts applied) of selected muons 100% of the muons fulll this timing cut. Muons originating from cosmic ray showers are an irreducible background for every analysis dealing with muons. Cosmic muons tend to be well measured in the Muon System and the tracker, so even after several cuts on the quality of the p T measurement, and after timing cuts, some cosmic muons present at the time of the event can not be anticipated. Especiallyinthehigh-p T regionwheremuonsfromthevertexaremostlyduetoabadtrack t, thecosmiccontaminationbecomesoneofthemajorbackgrounds. NexttoNewPhysics and bad tracks, cosmic rays are the most probable source of muons with p T > 200 GeV, which pass all selection criteria. A track which obviously does not originate from the vertex will not pass the track quality criteria discussed below. Therefore, cuts requiring a well measured track implicitly also perform a very loose cut on 1 cm (distance-ofclosest-approach) . As a consequence no additional anti-cosmic dca-cut is made to remain sensitive to possible secondary vertex decays of new particles. As for the electron candidate, a cut on the dierence between z-coordinate of the muon candidate and z-coordinate of the primary vertex is made. In this way all leptons belong to the same vertex, and badly reconstructed tracks or vertices are discarded. As discussed earlier, the p T -measurement is performed by the tracker. In order to ensure a precise measurement of the central track, the Silicon Vertex Detector is mandatory. The relative error of p T increases with p T , and tracks without SMT-hits have even worse resolution (see Figure 2.7). Poorly measured tracks have a much larger probability of producing a very high p T measurement (> 200 GeV). By requiring at least three SMT-hits, a three-dimensionaltrackreconstructionispossible. Theresultingsagitta(p T )measurement using the Silicon Vertex Detector has a better resolution, and the non-physical high-p T - background is reduced. 100% of muons reconstructed with the SMT cut have more than
Page 1: Model Independent Search for Deviat
Page 4 and 5: Contents 4 The Data Sample and Obje
Page 7 and 8: Introduction Science attempts to de
Page 10 and 11: 4 The Theoretical Foundations 1.1.2
Page 12 and 13: 6 The Theoretical Foundations e - e
Page 14 and 15: 8 The Theoretical Foundations Figur
Page 16 and 17: 10 The Theoretical Foundations Figu
Page 18 and 19: 12 The Theoretical Foundations 1.3
Page 20 and 21: 14 The Theoretical Foundations cont
Page 22 and 23: 16 Tevatron and the DØ-Detector Fi
Page 28 and 29: 22 Tevatron and the DØ-Detector 1/
Page 30 and 31: 24 Tevatron and the DØ-Detector 2.
Page 32 and 33: 26 Tevatron and the DØ-Detector of
Page 35 and 36: Chapter 3 The Concept of Model Inde
Page 37 and 38: 3.2. Concept 31 viations from SM. T
Page 39: 3.2. Concept 33 cal problem as many
Page 42 and 43: 36 The Data Sample and Object Ident
Page 50 and 51: muon_trackchi_pt_py Entries 5727 mu
Page 54 and 55: jet_eta_phi_px Entries 29768 Mean j
Page 57 and 58: Chapter 5 Monte Carlo Samples 5.1 M
Page 59 and 60: 5.1. MC Generator 53 Figure 5.3: Sc
Page 61 and 62: 5.2. SM-Processes 55 SM-process (M
Page 63 and 64: 5.3. Energy Scale and Smearing 57 J
Page 65: 5.3. Energy Scale and Smearing 59 e
Page 68 and 69: 62 General Data↔MonteCarlo Compar
Page 96 and 97: 90 Search Algorithm oer sucient sen
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92 Search Algorithm probability 0.0
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94 Search Algorithm 7.2.2 The Princ
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Chapter 8 Systematic Uncertainties
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8.3. QCD-Background 99 Whendicingda
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8.5. Smearing 101 Here N j i (σ+ )
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8.6. Summary of the Different Contr
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106 Results and Interpretation Figu
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108 Results and Interpretation Even
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110 Results and Interpretation even
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112 Results and Interpretation Anat
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114 Results and Interpretation To c
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116 Results and Interpretation Resu
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120 Results and Interpretation Even
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124 Results and Interpretation Resu
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Chapter 10 Conclusion In this diplo
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Appendix A Trigger Denitions Electr
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131 Muon-triggers for lists up to v
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134 Bibliography [19] A. Aktas et a
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Acknowledgements So, the end is nea
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