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

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measurement of the bunch charge product n1n2, the luminosity can be extracted from Equation 3.5. The σvis can be accordingly determined by comparing this peak luminosity to the peak interaction rate, µ MAX vis , observed during the vdM scan when the beams are unseparated: σvis = µ MAX vis 2πΣxΣy , (3.6) In the limit µvis ≪ 1, µvis is a linear function of the event rate, as µvis increases it must be calculated taking n1n2 into account Poisson statistics, and in some cases, instrumental and pile-up effects. Three different types of luminosity determination techniques can be listed: Event counting: determining the fraction of BC where an “event” (for a given selection requirement) was registered by the detector. Hit counting: counting number of hits per BC in a given detector. Particle counting: assessing the distribution of the number of particles per beam crossing inferred from any observable that reflects the instantaneous particle flux transversing the detector. For event counting algorithms there are two main types being used in ATLAS: inclusive (EventOR) and coincidence (EventAND) counting. More specifically ATLAS currently uses the following detectors and algorithms: • LUCID EventAND • LUCID EventOR • BCM EventOR • MBTS Timing (EventAND algorithm with a timing constraint) • PrimVtx (number of events with a primary vertex containing at least four tracks with pT > 150 MeV). The last two are offline algorithms relying in the MBTS detector, and the vertexing capabilities of the inner detector, respectively. In both inclusive and coincide counting types it is assumed that the efficiency to detect an inelastic pp interaction is constant, in the sense that it does not change when several interactions occur in the same BC. The relevant efficiencies for these two types are: ε A and ε C , for observing an event with, respectively, at 37
least one hit on the A-side, at least one hit on the C-side, and ε OR and ε AND , for observing at least one hit on both sides simultaneously, at least one hit on either side, respectively. These efficiencies are related by ε OR = ε A + ε C − ε AND . In an EventOR algorithm, a BC is counted if the sum of all hits on both the forward (A) and backward (C) arms of the detector being used is at least one. Since the Poisson probability of observing zero events OR −µε in a given bunch is P0 µ vis = e OR = e−µOR vis , then, the probability of observing an inclusive event can be computed as: PEvent OR OR −µ µ vis = 1 − e OR vis = NOR . (3.7) Here NOR is the number of BCs, in a given time interval, in which at least one pp interaction satisfies the event selection of the OR algorithm, and NBC is the total number of BCs in the same interval. From Equation 3.7 µ OR vis can be solved in terms of the event counting rate: NBC µ OR vis = −ln 1 − NOR . (3.8) NBC For the EventAND algorithm, a BC is counted if there is at least one hit in both sides of the detector. So, the probability of observing a coincidence event will be one minus the probability of there being no hit e−µεA, plus the e−µεC, minus the probability that there be no hit on on at least one side. This being the probability that there be no hit on at least side A probability that there be no hit on at least side C either side PEvent AND e −µεOR : AND µ vis = 1 − e µεA + e µεC − e µεOR = 1 − e µεA + e µεC − e µ(εA +ε C −ε AND ) = NAND NBC For using such a coincidence algorithm in detectors like LUCID and BCM, the fact that ε AND ≪ ε A,C can be used, along with the assumption that ε A ≈ ε C , to simplify Equation 3.9: PEvent AND AND NAND µ vis = NBC = 1 − 2e −µ(εAND +ε OR )/2 + e µε OR (3.9) = 1 − 2e −(1+σOR vis /σAND vis )µ AND vis /2 + e −(σOR vis /σAND vis )µ AND vis (3.10) where εOR = σOR vis σAND ε vis AND has been used. This expression can not be inverted analytically to determine µ AND vis . It can, however, be solved numerically. If the efficiency is high and ε AND ≈ ε A ≈ ε C as in the case of coincide 38
Page 1 and 2: CERN-THESIS-2012-153 26/07/2012 c
Page 3 and 4: Abstract A search for flavor-changi
Page 5 and 6: Acknowledgments I first want to tha
Page 7 and 8: Table of Contents List of Tables .
Page 9 and 10: List of Tables 2.1 The fundamental
Page 11 and 12: List of Figures 2.1 The potential V
Page 13 and 14: 5.15 Distributions of the 3ID analy
Page 15 and 16: This thesis is organized as follows
Page 17 and 18: the question whether each neutrino
Page 19 and 20: gauge invariant field strength tens
Page 21 and 22: for strong interactions. Although W
Page 23 and 24: particles. Because of the introduct
Page 25 and 26: which is introduced for mass genera
Page 27 and 28: 2.3 Top Quark The large mass of the
Page 29 and 30: ATLAS Preliminary Data 2011 Channel
Page 31 and 32: as the masses of the quarks involve
Page 33 and 34: LEP HERA Tevatron LHC BR(t → qγ)
Page 35 and 36: to Wtb couplings, where limits on a
Page 37 and 38: tion at the collision point, and F
Page 39 and 40: The positive x-direction is defined
Page 41 and 42: large air-core toroids (one barrel
Page 43 and 44: 3.3.3 Calorimetry The calorimetry i
Page 45 and 46: of ∼ 1% for the H → γγ and H
Page 47 and 48: esolution of 1 cm×1 ns with digita
Page 49: Luminosity measurement Accurate det
Page 53 and 54: caps. The calorimeter selections ar
Page 55 and 56: ut instead fragment to color neutra
Page 57 and 58: Decays A large fraction of the part
Page 59 and 60: The ALGPEN program with HERWIG show
Page 61 and 62: Normalized to unit / 1.96429 GeV No
Page 63 and 64: Chapter 5 Event Selection 5.1 Intro
Page 65 and 66: Variable Cut pT >20 GeV Type MuID t
Page 67 and 68: Identification efficiency eff id 1
Page 69 and 70: (a) (b) Figure 5.4: Electron identi
Page 71 and 72: ε (P ) µ TL T 1 TL µ ε TL µ ε
Page 73 and 74: Jets in this analysis are reconstru
Page 75 and 76: impact parameter significance of we
Page 77 and 78: event is also discarded. Events wit
Page 79 and 80: event kinematics, however no b-jet
Page 81 and 82: Events / 10 GeV trackleptons / 10
Page 83 and 84: analysis, is 22%. Figure 5.13(a) sh
Page 85 and 86: transverse momentum of the leading
Page 87 and 88: Events / 10 GeV Events / 10 GeV 14
Page 89 and 90: two background sources, diboson and
Page 91 and 92: ID leptons provides three different
Page 93 and 94: 3ID Final Selection ZZ and WZ 9.5
Page 95 and 96: data, has systematic uncertainties
Page 97 and 98: Jets The jet energy scale (JES) and
Page 99 and 100: the fake prediction was scaled down
Page 101 and 102:
two or more, and events with E miss
Page 103 and 104:
Source MC Background Luminosity ±
Page 105 and 106:
Chapter 8 Limit Evaluation 8.1 Intr
Page 107 and 108:
means: Q = L( X,s + b) L( , (8.5)
Page 109 and 110:
computed from Equation 8.12 replaci
Page 111 and 112:
Chapter 9 Conclusions A search for
Page 113 and 114:
There are a total of 666236 γ+jets
Page 115 and 116:
Appendix B Backgrounds to the 3ID a
Page 117 and 118:
Appendix C Systematic Uncertainties
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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