CERN-THESIS-2012-153 26/07/2012 - CERN Document Server

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Z-boson decay, in which one of the jets is misidentified as the third lepton. To evaluate this background a DD method was developed. This method uses a control region (CR) in the (E miss T ,mℓℓ) plane by selecting events with two opposite-charge electrons or muons with invariant mass satisfying |91.19 GeV − m reco ℓℓ | < 15 GeV. This is done in six different regions of E miss T , from 0 GeV to ≥50 GeV. The Z+jets estimate in the SR, in each E miss T For each E miss T bin, is simply given by: data NZ+jets SR = data MC N − Nother bkg. NMC · Z+jets CR N MC Z+jets . (B.1) SR bin considered, the corresponding normalization factor (background-subtracted data to simulation ratio in the CR) is obtained and applied to the simulated Z+jets background in the SR. Applying the multiplicative factor quoted above, this gives the expected number of Z+jets events in the data. The contribution of the remaining processes to the one fake lepton background (dileptonic t¯t, Wt-channel single top, WW production) is evaluated using MC simulation samples with the loose lepton selection and the scale factor from above. A DD method was developed to evaluate the contribution from multijet, W+jets, single top and t¯t single lepton decay events, in which two or three jets are reconstructed as leptons (2+3 fake leptons). Due to the requirements that two leptons should have the same flavor and opposite charges, the yield from these background sources can be extrapolated from the number of observed data events with three leptons of any flavor (e and µ), but with the same charge. Taking into account the possible charge and flavor combinations, there are 36 combinations of three leptons, in which two have the same flavor and opposite charges, and 16 combinations of three leptons with the same charge. The extrapolation factor is thus f = 36/16 = 2.25. No data events passed the selection after requiring three leptons with the same charge. The uncertainties in the DD backgrounds are determined using the Feldman-Cousins upper interval for a 68% CL [109] with no observed events (with the uncertainties multiplied by 2.25 for the 2+3 fake leptons sample). Since no events with three leptons of the same charge are selected, a multiplicative factor of 0.<strong>07</strong> ± 0.018, to account for the final requirements of at least two ID jets and E miss T uncertainty estimate. > 20 GeV, is evaluated using MC and applied to the The yields of the expected background and the data observation for the final selection of the 3ID selection were presented in Chapter 6. 103
Appendix C Systematic Uncertainties in the 3ID analysis For the 3ID channel the dominant source of systematic uncertainty is the ZZ and WZ simulation modelling. Other sources have effects at most of the same magnitude as the statistical uncertainty. Table C.1 shows a summary of the different uncertainties and their contribution to the net background yields and signal acceptance in the 3ID analysis. 104
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CERN-THESIS-2012-153 26/07/2012 c
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Abstract A search for flavor-changi
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Acknowledgments I first want to tha
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Table of Contents List of Tables .
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List of Tables 2.1 The fundamental
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List of Figures 2.1 The potential V
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5.15 Distributions of the 3ID analy
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This thesis is organized as follows
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the question whether each neutrino
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gauge invariant field strength tens
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for strong interactions. Although W
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particles. Because of the introduct
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which is introduced for mass genera
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2.3 Top Quark The large mass of the
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ATLAS Preliminary Data 2011 Channel
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as the masses of the quarks involve
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LEP HERA Tevatron LHC BR(t → qγ)
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to Wtb couplings, where limits on a
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tion at the collision point, and F
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The positive x-direction is defined
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large air-core toroids (one barrel
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3.3.3 Calorimetry The calorimetry i
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of ∼ 1% for the H → γγ and H
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esolution of 1 cm×1 ns with digita
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Luminosity measurement Accurate det
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least one hit on the A-side, at lea
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caps. The calorimeter selections ar
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ut instead fragment to color neutra
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Decays A large fraction of the part
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The ALGPEN program with HERWIG show
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Normalized to unit / 1.96429 GeV No
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Chapter 5 Event Selection 5.1 Intro
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Page 97 and 98: Jets The jet energy scale (JES) and
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Page 105 and 106: Chapter 8 Limit Evaluation 8.1 Intr
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Page 111 and 112: Chapter 9 Conclusions A search for
Page 113 and 114: There are a total of 666236 γ+jets
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Page 119 and 120: References [1] J. L. Borges, Tres v
Page 121 and 122: [40] G. Lu, F. Yin, X. Wang and L.
Page 123 and 124: [82] ATLAS Collaboration, Expected
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