In 2010, the Large Hadron Collider (\\lhc{}) at the European Organisation for Nuclear Research (CERN) near Geneva (Switzerland) came into full operation providing proton-proton collisions at a centre-of-mass energy of $\\sqrt{s} = \\unit[7]{TeV}$. \\lhc{} data may allow the observation of the Higgs boson, the last unknown building block of the standard model of particle physics (SM). Di-muon final states containing heavy flavour jets pose an irreducible background for searches of the Higgs boson as predicted the SM or theories beyond. They also provide a unique testbed for tests of perturbative Quantum Chromo-Dynamics (pQCD). This thesis provides a measurement of the cross section of events with one di-muon pair with an invariant mass in the \\Z{} mass region and at least one heavy flavour jet. Studies on acceptance and systematic effects of the experimental setup are presented as well as a comparison to theoretical predictions. The total inclusive cross section of \\zbFS{} events was observed as $\\sigma(\\mu^{+}\\mu^{-}+b+X) = \\unit[(4.15 ^{+0.97}_{-0.89} (stat.) ^{+0.45}_{-0.53} (syst.))]{pb} $ from the equivalent of $\\unit[36]{pb^{-1}}$ of data. Agreement with pQCD predictions at next-to leading order (NLO) is found while tensions with leading order (LO) predictions are observed. Further, the cross-section ratio \\RwZ{} with events containing two muons and at least one jet of any origin was measured to $\\mathcal{R} = \\unit[4.6 ^{+1.4}_{-1.2} (stat.) \\pm 0.5 (syst.)]{\\%}$. This is found to agree with NLO and LO calculations within known uncertainties.

In this study, a measurement of the production cross section of Standard Model Z bosons in proton-proton collisions in the decay channel Z to tau tau is performed with data of 1.34 fb-1 - 1.55fb-1 recorded by the ATLAS experiment at the LHC at a center-of-mass energy of 7 TeV. An event selection of the data is applied in order to obtain a sample enriched with Z to tau tau events. After background estimations using data and Monte Carlo (MC) simulations, the fiducial cross sections in the sub-channels Z to tau tau to e tau_h + 3nu and Z to tau tau to mu tau_h + 3nu are measured. Together with the geometrical and kinematical acceptance, A_Z, and the well known tau lepton branching fractions, these results are combined to a total inclusive Z to tau tau cross section. A_Z is obtained from MC studies only, and the combination of the channels is done including statistical and systematical uncertainties using the BLUE method. The result is a measured total inclusive cross section of 914.4 plus minus 14.6(stat) plus minus 95.1(syst) plus minus 33.8(lumi) pb. This is in agreement with theoretical predictions from NNLO calculations of 964 plus minus 48 pb and also with measurements previously performed by the ATLAS and CMS experiments. With the increased amount of data, the statistical uncertainty could be reduced significantly compared to previous measurements. Furthermore, a testbeam analysis is performed to study the operation of the electromagnetic and hadronic endcap calorimeters, EMEC and HEC, and of the forward calorimeter, FCal, in the high particle fluxes expected for the upgraded LHC. The high voltage return currents of the EMEC module are analysed in dependence of the beam intensity. The results are compared to model predictions and simulations to extract the point of critical operation. Overall, the results for the critical beam intensities and the critical high voltage currents are in agreement with the predictions, but the assigned uncertainties are rather large. The general behaviour of the high voltage current in dependence of the beam intensity above the critical intensity could be confirmed very well. The testbeam data show that the EMEC can be operated up to highest LHC luminosities, and that ATLAS conserves its excellent calorimeter performance in this detector area.:Contents List of Figures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11 List of Tables. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14 1 Introduction. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17 2 Theoretical Foundation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19 2.1 The Standard Model of Particle Physics . . . . . . . . . . . . . . . . . . . . 19 2.1.1 Phenomenological Overview . . . . . . . . . . . . . . . . . . . . . . . 19 2.1.2 Quantum Electrodynamics . . . . . . . . . . . . . . . . . . . . . . . . 21 2.1.3 Electroweak Interaction . . . . . . . . . . . . . . . . . . . . . . . . . 23 2.1.4 Particle Masses and the Higgs Mechanism . . . . . . . . . . . . . . . 24 2.1.5 Quantum Chromo Dynamics . . . . . . . . . . . . . . . . . . . . . . . 27 2.2 Z Boson Production and Decay at the LHC . . . . . . . . . . . . . . . . . . 29 2.3 Event Generation and Simulation . . . . . . . . . . . . . . . . . . . . . . . . 31 2.3.1 The Partonic Process . . . . . . . . . . . . . . . . . . . . . . . . . . . 31 2.3.2 Hadronization . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33 2.3.3 The Underlying Event . . . . . . . . . . . . . . . . . . . . . . . . . . 33 2.3.4 Detector Simulation . . . . . . . . . . . . . . . . . . . . . . . . . . . 33 2.4 Cross Section Predictions for Z Boson Production at the LHC . . . . . . . . 34 3 The LHC and the ATLAS Experiment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37 3.1 The Large Hadron Collider . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37 3.2 The ATLAS Experiment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39 3.2.1 The Inner Detector . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41 3.2.2 The Electromagnetic Calorimeter . . . . . . . . . . . . . . . . . . . . 42 3.2.3 The Hadronic Calorimeter . . . . . . . . . . . . . . . . . . . . . . . . 47 3.2.4 The Muon Spectrometer . . . . . . . . . . . . . . . . . . . . . . . . . 48 3.2.5 Luminosity Measurement . . . . . . . . . . . . . . . . . . . . . . . . . 49 3.2.6 The Trigger System . . . . . . . . . . . . . . . . . . . . . . . . . . . . 51 3.2.7 Data Taking . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 52 4 Testbeam Study of Liquid-Argon Calorimeter Performance at High Rates . . . . 55 4.1 Upgrade Plans of the LHC and the ATLAS Calorimeters . . . . . . . . . . . 55 4.2 Testbeam Parameters and Setup . . . . . . . . . . . . . . . . . . . . . . . . . 56 4.3 The Calorimeter Test Modules . . . . . . . . . . . . . . . . . . . . . . . . . . 58 4.4 Test Module Readout and Signal Degradation . . . . . . . . . . . . . . . . . 58 4.5 Measurement and Analysis of the HV Currents . . . . . . . . . . . . . . . . . 61 4.5.1 Device for Precision HV Current Measurement . . . . . . . . . . . . . 62 4.5.2 Testbeam Data Taking . . . . . . . . . . . . . . . . . . . . . . . . . . 62 4.5.3 Analysis of the EMEC Currents . . . . . . . . . . . . . . . . . . . . . 63 4.5.4 Beam Intensity Measurement . . . . . . . . . . . . . . . . . . . . . . 65 4.5.5 Comparison of EMEC Currents to Beam Intensity . . . . . . . . . . . 67 4.5.6 Discussion Considering the Predictions . . . . . . . . . . . . . . . . . 72 4.6 Summary of Results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 74 5 Z → τ τ Cross Section Measurement with 1.34-1.55 fb−1 . . . . . . . . . . . . . . . . . . . . 75 5.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 75 5.2 Data and Monte Carlo Samples . . . . . . . . . . . . . . . . . . . . . . . . . 75 5.2.1 Trigger Requirements . . . . . . . . . . . . . . . . . . . . . . . . . . . 76 5.2.2 Monte Carlo Simulations . . . . . . . . . . . . . . . . . . . . . . . . . 76 5.2.3 Pile-up Simulation . . . . . . . . . . . . . . . . . . . . . . . . . . . . 77 5.2.4 Tau Trigger Weighting . . . . . . . . . . . . . . . . . . . . . . . . . . 78 5.3 Event Preselection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 78 5.3.1 Good Run List . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 78 5.3.2 Vertex Requirement . . . . . . . . . . . . . . . . . . . . . . . . . . . . 79 5.3.3 Calorimeter Jet Cleaning . . . . . . . . . . . . . . . . . . . . . . . . . 80 5.3.4 Liquid-Argon Calorimeter Hole Cleaning . . . . . . . . . . . . . . . . 80 5.4 Reconstructed Physics Objects . . . . . . . . . . . . . . . . . . . . . . . . . . 81 5.4.1 Muons . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 82 5.4.2 Electrons . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 82 5.4.3 Jets . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 84 5.4.4 Taus . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 84 5.4.5 Missing Transverse Energy . . . . . . . . . . . . . . . . . . . . . . . . 86 5.4.6 Overlap Removal . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 87 5.5 Event Selection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 88 5.5.1 Dilepton Veto . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 88 5.5.2 Opposite Charge Between the Lepton and the Hadronic Tau Candidate 89 5.5.3 Reduction of W+jets Background . . . . . . . . . . . . . . . . . . . . 89 5.5.4 Final Requirements on the Tau Candidate . . . . . . . . . . . . . . . 90 5.5.5 Visible Mass Window . . . . . . . . . . . . . . . . . . . . . . . . . . . 91 5.5.6 Summary of the Event Selection . . . . . . . . . . . . . . . . . . . . . 92 5.6 Tau Identification Variables . . . . . . . . . . . . . . . . . . . . . . . . . . . 96 5.7 Background Estimation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 99 5.7.1 W+jets . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 99 5.7.2 Z+jets . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 100 5.7.3 QCD Multijet Events . . . . . . . . . . . . . . . . . . . . . . . . . . . 102 5.8 Cross Section Measurement . . . . . . . . . . . . . . . . . . . . . . . . . . . 103 5.9 Systematic Uncertainties . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 106 5.9.1 Trigger Efficiencies and Scale Factors . . . . . . . . . . . . . . . . . . 106 5.9.2 Reconstruction, Identification and Isolation Efficiencies of the Muons and Electrons . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 107 5.9.3 Identification Efficiency of the Hadronically Decaying Tau . . . . . . 108 5.9.4 Background Estimation . . . . . . . . . . . . . . . . . . . . . . . . . . 109 5.9.5 Geometrical and Kinematical Acceptance AZ . . . . . . . . . . . . . 110 5.9.6 Energy Scale Uncertainty . . . . . . . . . . . . . . . . . . . . . . . . 111 5.9.7 Further Systematic Uncertainties . . . . . . . . . . . . . . . . . . . . 112 5.9.8 Summary of Systematic Uncertainties . . . . . . . . . . . . . . . . . . 112 5.10 Combination of the Channels and Results . . . . . . . . . . . . . . . . . . . 112 5.11 The Z → τ τ Cross Section Measurement in the LHC Physics Context . . . . 115 6 Summary and Outlook . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 121 A Gauge Invariance in Quantum Electrodynamics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 123 A.1 Local gauge invariance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 123 A.2 Gauge invariance of the Maxwell-Equations . . . . . . . . . . . . . . . . . . . 123 B Testbeam Results. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 125 C Tau Trigger Weighting . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 131 C.1 Event Selection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 131 C.2 Tau Trigger Efficiency Measurement . . . . . . . . . . . . . . . . . . . . . . . 132 C.3 Systematic Uncertainties . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 133 Bibliography. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 135 / In dieser Studie wird eine Wirkungsquerschnittsmessung des Standardmodell-Z-Bosons im Zerfallskanal Z nach tau tau mit Kollisionsereignissen entsprechend 1.34 fb-1 bis 1.55 fb-1 aufgezeichneter Daten des ATLAS-Experiments am LHC bei einer Schwerpunktsenergie von 7 TeV durchgefuehrt. Hierbei kommt eine spezielle Ereignisselektion der Daten zum Einsatz, die zum Ziel hat, einen mit Z nach tau tau Ereignissen angereicherten Datensatz zu erhalten. Nach einer Untergrundabschaetzung mit Hilfe von experimentellen Daten und Monte-Carlo(MC)-Simulationen wird eine spezifische Wirkungsquerschnittsmessung in den Unterkanaelen Z nach tau tau nach e tau_h + 3nu und Z nach tau tau nach mu tau_h + 3nu erreicht, welche zunaechst nur Ereignisse in der geometrischen und kinematischen Akzeptanzregion umfasst. Zusammen mit der Selektionseffizienz dieser Akzeptanzregion, A_Z, und den bekannten Tau-Lepton-Verzweigungsverhaeltnissen koennen diese Ergebnisse zu einem totalen, inklusiven Z nach tau tau Wirkungsquerschnitt kombiniert werden. Hierbei wird A_Z ausschliesslich aus MC-Studien bestimmt und die Kombination unter Beruecksichtigung der statistischen und systematischen Fehler der Einzelkanaele mit der BLUE-Methode durchgefuehrt. Das Ergebnis ist ein totaler, inklusiver Wirkungsquerschnitt von 914.4 plus minus 14.6(stat) plus minus 95.1(syst) plus minus 33.8(lumi) pb. Dies stimmt innerhalb der Messunsicherheiten sowohl mit theoretischen Vorhersagen aus NNLO Rechnungen von: 964 plus minus 48 pb als auch mit Messungen, die zuvor im Zuge der ATLAS- und CMS-Experimente durchgefuehrt wurden, ueberein. Im Vergleich zu den bisherigen Messungen koennen die statistischen Fehler mit dem groesseren Datensatz deutlich reduziert werden. Weiterhin wird eine Teststrahlstudie zur Pruefung der Funktionalitaet der elektromagnetischen und hadronischen Endkappenkalorimeter, EMEC und HEC, und des Vorwaertskalorimeters FCal in den zukuenftigen, hohen Teilchenflussdichten des verbesserten LHC praesentiert. Die Hochspannungsstroeme des EMEC-Moduls werden in Abhaengigkeit von der Strahlintensitaet analysiert. Weiterhin werden die Ergebnisse mit Modellvorhersagen und Simulationen verglichen, um die Punkte nichtlinearen (kritischen) Betriebes zu extrahieren. Die Ergebnisse fuer die kritische Strahlintensitaet und die kritischen Stroeme stimmen mit Modellrechnungen und Simulationen ueberein, die jedoch mit grossen Unsicherheiten behaftet sind. Das vorhergesagte Verhalten der Hochspannungsstroeme in Abhaengigkeit von der Strahlintensitaet oberhalb der kritischen Intensitaet konnte sehr genau bestaetigt werden. Die Teststrahldaten zeigen, dass das EMEC bis zu den hoechsten LHC-Luminositaeten arbeiten kann und ATLAS in dieser Detektorregion seine exzellenten Kalorimetereigenschaften beibehaelt.:Contents List of Figures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11 List of Tables. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14 1 Introduction. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17 2 Theoretical Foundation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19 2.1 The Standard Model of Particle Physics . . . . . . . . . . . . . . . . . . . . 19 2.1.1 Phenomenological Overview . . . . . . . . . . . . . . . . . . . . . . . 19 2.1.2 Quantum Electrodynamics . . . . . . . . . . . . . . . . . . . . . . . . 21 2.1.3 Electroweak Interaction . . . . . . . . . . . . . . . . . . . . . . . . . 23 2.1.4 Particle Masses and the Higgs Mechanism . . . . . . . . . . . . . . . 24 2.1.5 Quantum Chromo Dynamics . . . . . . . . . . . . . . . . . . . . . . . 27 2.2 Z Boson Production and Decay at the LHC . . . . . . . . . . . . . . . . . . 29 2.3 Event Generation and Simulation . . . . . . . . . . . . . . . . . . . . . . . . 31 2.3.1 The Partonic Process . . . . . . . . . . . . . . . . . . . . . . . . . . . 31 2.3.2 Hadronization . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33 2.3.3 The Underlying Event . . . . . . . . . . . . . . . . . . . . . . . . . . 33 2.3.4 Detector Simulation . . . . . . . . . . . . . . . . . . . . . . . . . . . 33 2.4 Cross Section Predictions for Z Boson Production at the LHC . . . . . . . . 34 3 The LHC and the ATLAS Experiment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37 3.1 The Large Hadron Collider . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37 3.2 The ATLAS Experiment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39 3.2.1 The Inner Detector . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41 3.2.2 The Electromagnetic Calorimeter . . . . . . . . . . . . . . . . . . . . 42 3.2.3 The Hadronic Calorimeter . . . . . . . . . . . . . . . . . . . . . . . . 47 3.2.4 The Muon Spectrometer . . . . . . . . . . . . . . . . . . . . . . . . . 48 3.2.5 Luminosity Measurement . . . . . . . . . . . . . . . . . . . . . . . . . 49 3.2.6 The Trigger System . . . . . . . . . . . . . . . . . . . . . . . . . . . . 51 3.2.7 Data Taking . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 52 4 Testbeam Study of Liquid-Argon Calorimeter Performance at High Rates . . . . 55 4.1 Upgrade Plans of the LHC and the ATLAS Calorimeters . . . . . . . . . . . 55 4.2 Testbeam Parameters and Setup . . . . . . . . . . . . . . . . . . . . . . . . . 56 4.3 The Calorimeter Test Modules . . . . . . . . . . . . . . . . . . . . . . . . . . 58 4.4 Test Module Readout and Signal Degradation . . . . . . . . . . . . . . . . . 58 4.5 Measurement and Analysis of the HV Currents . . . . . . . . . . . . . . . . . 61 4.5.1 Device for Precision HV Current Measurement . . . . . . . . . . . . . 62 4.5.2 Testbeam Data Taking . . . . . . . . . . . . . . . . . . . . . . . . . . 62 4.5.3 Analysis of the EMEC Currents . . . . . . . . . . . . . . . . . . . . . 63 4.5.4 Beam Intensity Measurement . . . . . . . . . . . . . . . . . . . . . . 65 4.5.5 Comparison of EMEC Currents to Beam Intensity . . . . . . . . . . . 67 4.5.6 Discussion Considering the Predictions . . . . . . . . . . . . . . . . . 72 4.6 Summary of Results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 74 5 Z → τ τ Cross Section Measurement with 1.34-1.55 fb−1 . . . . . . . . . . . . . . . . . . . . 75 5.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 75 5.2 Data and Monte Carlo Samples . . . . . . . . . . . . . . . . . . . . . . . . . 75 5.2.1 Trigger Requirements . . . . . . . . . . . . . . . . . . . . . . . . . . . 76 5.2.2 Monte Carlo Simulations . . . . . . . . . . . . . . . . . . . . . . . . . 76 5.2.3 Pile-up Simulation . . . . . . . . . . . . . . . . . . . . . . . . . . . . 77 5.2.4 Tau Trigger Weighting . . . . . . . . . . . . . . . . . . . . . . . . . . 78 5.3 Event Preselection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 78 5.3.1 Good Run List . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 78 5.3.2 Vertex Requirement . . . . . . . . . . . . . . . . . . . . . . . . . . . . 79 5.3.3 Calorimeter Jet Cleaning . . . . . . . . . . . . . . . . . . . . . . . . . 80 5.3.4 Liquid-Argon Calorimeter Hole Cleaning . . . . . . . . . . . . . . . . 80 5.4 Reconstructed Physics Objects . . . . . . . . . . . . . . . . . . . . . . . . . . 81 5.4.1 Muons . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 82 5.4.2 Electrons . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 82 5.4.3 Jets . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 84 5.4.4 Taus . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 84 5.4.5 Missing Transverse Energy . . . . . . . . . . . . . . . . . . . . . . . . 86 5.4.6 Overlap Removal . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 87 5.5 Event Selection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 88 5.5.1 Dilepton Veto . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 88 5.5.2 Opposite Charge Between the Lepton and the Hadronic Tau Candidate 89 5.5.3 Reduction of W+jets Background . . . . . . . . . . . . . . . . . . . . 89 5.5.4 Final Requirements on the Tau Candidate . . . . . . . . . . . . . . . 90 5.5.5 Visible Mass Window . . . . . . . . . . . . . . . . . . . . . . . . . . . 91 5.5.6 Summary of the Event Selection . . . . . . . . . . . . . . . . . . . . . 92 5.6 Tau Identification Variables . . . . . . . . . . . . . . . . . . . . . . . . . . . 96 5.7 Background Estimation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 99 5.7.1 W+jets . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 99 5.7.2 Z+jets . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 100 5.7.3 QCD Multijet Events . . . . . . . . . . . . . . . . . . . . . . . . . . . 102 5.8 Cross Section Measurement . . . . . . . . . . . . . . . . . . . . . . . . . . . 103 5.9 Systematic Uncertainties . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 106 5.9.1 Trigger Efficiencies and Scale Factors . . . . . . . . . . . . . . . . . . 106 5.9.2 Reconstruction, Identification and Isolation Efficiencies of the Muons and Electrons . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 107 5.9.3 Identification Efficiency of the Hadronically Decaying Tau . . . . . . 108 5.9.4 Background Estimation . . . . . . . . . . . . . . . . . . . . . . . . . . 109 5.9.5 Geometrical and Kinematical Acceptance AZ . . . . . . . . . . . . . 110 5.9.6 Energy Scale Uncertainty . . . . . . . . . . . . . . . . . . . . . . . . 111 5.9.7 Further Systematic Uncertainties . . . . . . . . . . . . . . . . . . . . 112 5.9.8 Summary of Systematic Uncertainties . . . . . . . . . . . . . . . . . . 112 5.10 Combination of the Channels and Results . . . . . . . . . . . . . . . . . . . 112 5.11 The Z → τ τ Cross Section Measurement in the LHC Physics Context . . . . 115 6 Summary and Outlook . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 121 A Gauge Invariance in Quantum Electrodynamics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 123 A.1 Local gauge invariance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 123 A.2 Gauge invariance of the Maxwell-Equations . . . . . . . . . . . . . . . . . . . 123 B Testbeam Results. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 125 C Tau Trigger Weighting . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 131 C.1 Event Selection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 131 C.2 Tau Trigger Efficiency Measurement . . . . . . . . . . . . . . . . . . . . . . . 132 C.3 Systematic Uncertainties . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 133 Bibliography. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 135

Adolescents involvement in societal issues has been found to be able to influence companies.  Simultaneously, a growing interest in today’s consumers has been found to include ethical commitments in their consumption, a trend considered to be driven by young consumers. This can put an immense pressure on companies to take on a greater responsibility in societal issues. Young consumers in the year 2020 are considered to belong to Generation Z, a consumer group described as conscious and driven by topics of social development, predicted to possess future purchasing dominance. Whether or not Generation Z views consumption as a matter of involving ethical considerations could be of great importance to consider in order to attract the highly influential consumer group. The consequences for not taking this into consideration could result in not being able to reach out to the consumer group properly. Research has sought to understand ethical consumption in regards to generational and cultural differences. This study aims to expand the existing research area on ethical consumption in relation to Generation Z by implementing a focus on Swedish consumers within Generation Z. The purpose of this study is to attain a deeper understanding of how Generation Z’s consumption is influenced by ethical considerations. This has been done by including a theoretical background on ethical consumption, the buying decision process as well as Generation Z. Given the background and purpose of this study, it is of interest to examine how Generation Z is influenced by ethical considerations in their purchase decision. Through a qualitative research method and cross-sectional design, focus group interviews were conducted together with individuals within Generation Z. The empirical evidence from the study shows that Generation Z are influenced by ethical considerations, but not to the extent that it is conclusive for their purchase decision. The factors for purchasing an ethical product include regarding the ethical symbol as visually appealing, trusting the ethical labelling, having sufficient knowledge regarding the ethical stance, regarding the ethical stance as in line with their morals and values as well as their perceived price sensitivity for the ethical product. / Ungdomars engagemang i samhällsfrågor har visat sig kunna sätta prägel på och influera företag. Samtidigt är ett växande intresse för dagens konsumenter att inkludera etiska åtaganden i sin konsumtion, en trend som betraktas vara driven av unga konsumenter. Detta kan sätta stor press på företag att uppvisa ett större ansvarstagande i viktiga samhällsfrågor. År 2020 betraktas unga konsumenter tillhöra Generation Z, en konsumentgrupp med stor framtida köpdominans som beskrivs som medvetna och drivna kring frågor om samhällets utveckling. För företag som vill attrahera kundgruppen kan det vara av stor betydelse att beakta om huruvida Generation Z ser på konsumtion som en fråga om etiska överväganden. Konsekvensen som tillkommer för företag som inte väljer att beakta detta kan härleda till att de inte lyckas nå ut till konsumentgruppen. Tidigare forskning har försökt få en ökad förståelse för etisk konsumtion utifrån generationella och kulturella skillnader. Denna studie ämnar att vidga det befintliga forskningsområdet rörande etisk konsumtion i relation till Generation Z genom ett fokus på svenska konsumenter inom Generation Z. Studiens syfte är att få en ökad förståelse för hur Generation Z påverkas av etiska ställningstaganden vid konsumtion. Detta görs genom en teoretisk fördjupning inom etisk konsumtion, konsumentens köpbeslutsprocess samt Generation Z. Med given problembakgrund och syfte ämnar studien därför att utifrån forskningsfrågan undersöka hur Generation Z påverkas av etiska överväganden i deras köpbeslut. Utifrån en kvalitativ forskningsinriktning och tvärsnittsdesign genomfördes fokusgruppsintervjuer tillsammans med individer inom Generation Z. Empirin påvisar att Generation Z påverkas av etiska överväganden, men inte i den utsträckning att det alltid är avgörande för ett köpbeslut. De avgörande faktorerna för köp av en etisk produkt var om den etiska symbolen var visuellt tilltalande, om de hade förtroende för det etiska budskapet, om de upplevde att de hade tillräckligt med kunskap kring det etiska ställningstagandet, om det etiska ställningstagandet stämde överens med deras moral och värderingar samt deras upplevda priskänslighet för den etiska produkten.

I media framställs Generation Z som en miljömedveten generation som kan tänkas ha Greta Thunberg som förebild eftersom hon blivit en symbol för miljönrörelsen. Trots att undersökningar visar att Generation Z intresserar sig mer för miljöfrågor och etiska frågor entydigare generationer så finns det forskning som hävdar att generationen är oengagerade, egoistiska och konsumistiska. Uppsatsens syfte är att studera individer i Generation Z:sattityder till hållbart mode och huruvida dessa attityder speglar deras intentioner till hållbarkonsumtion. Avsikten med studien är att få en ökad förståelse till hur ett eventuellt gap mellanattityd och agerande kan förklaras. För att få en djupare förståelse för hur individernas attityder formas samt hur den speglar deras agerande används Trekomponentsmodellen som teoretiskt perspektiv i studien. Det empiriska materialet har samlats in genom en kvalitativmetod i form av tre fokusgrupper där svenska individer i Generation Z deltog. De teman som uppkom under kodningen har kopplats ihop med Trekomponentsmodellen som består av komponenterna uppfattning, känsla och beteende. Resultatet i vår studie tyder på att den viktigaste komponenten till den tvetydigheten som finns hos individerna i Generation Z verkar vara sociala medier. Empirin tyder på en kunskapsbrist, egoism, lathet och bristande engagemang är orsakerna till hur respondenternas agerar. Intervjupersonerna anser att det inte är dem som bär ansvaret för miljön och de hävdaratt miljökrisen ännu inte drabbat dem. Analysen visar även att när de väl konsumerar hållbart är intentionen aldrig att handla hållbart och att mycket av deras attityder till hållbart modeformas utifrån sociala medier. Slutsatsen kan därför dras att sociala medier är den största orsaken till deras attityder och beteende eftersom det visar sig att sociala medier även påverkar det som ligger till grund för deras attityder. Attityderna till respondenterna i denna studie skiljer sig från det Greta står för vilket kan tänkas bero på att hennes attityder speglar hennes agerande. Hennes hållbara attityder och agerande påverkas inte på samma sätt utifrån vad som sägs på sociala medier utan hon använder sociala medier för att nå ut med sinaåsikter. Då denna studie endast är gjord på individer i Generation Z kan resultatet inte generaliseras för en hel generation precis som Greta inte kan tala för en hel generation. Eftersom denna studie endast riktat in sig på tjejer i Generation Z skulle ett förslag till vidareforskning skulle vara att utföra samma studie fast på killar för att undersöka om resultaten skiljer sig. / In media, Generation Z is portrayed as environmentally conscious and that it could conceivably have Greta Thunberg as its role model since she has become a symbol for the environment. Although studies show that Generation Z has more interest in environmental and ethical issues than previous generations, there is also research that claims that the generation is unengaged, egoistic and consumeristic. The thesis purpose is therefore to study individuals in Generation Z’s attitudes towards sustainable fashion and whether these attitudes reflect their intentions towards sustainable consumption. The purpose of the study is to gain a greater understanding of how a possible gap between attitude and behavior can be explained. In order to gain a deeper understanding of how individuals' attitudes are shaped and how they reflect their actions, the three-component model is used as a theoretical perspective in this study. In this study, a qualitative method have been used where the empirical data was collected through three focus groups where swedish indiviuals in Generation Z participated. The themes that occurs during coding are then linked to the three-component model, which consists of perception, feelings and behaviour. The result of our study indicates that the most important component to this ambiguousness that exists among the individuals in Generation Z appears to be social media. The empirical data indicates that knowledge-deficiency, selfishness, indolence and lack of commitment are the reasons for the respondent’s actions. The respondents believe that it is not those who are responsible for the environment and they claim that the environmental crisis has not yet affected them. The result also shows that once they consume sustainably, the intention is never to act sustainably and that much of their attitudes towards sustainable fashion are shaped from social media. It can therefore be concluded that social media is the main cause of their attitudes and behaviour, as it turns out that social media also affects what underlies their attitudes. Unlike the respondents in this study, Greta Thunberg's attitudes and actions differ from those of the respondents since her attitudes reflect her actions. Her sustainable attitudes and actions cannot be changed based on what is being said on social media, instead she uses social media to reach out and get her voice heard. Since this study only focus on individuals in Generation Z, the result cannot be generalized for an entire generation just as Greta cannot speak for her entire generation. Since this study only focused on girls in Generation Z, one suggestion for further research could be to perform the same study on boys to see if the results differ.

Background: Brands have started paying attention to brand authenticity since consumer demand for authenticity is increasing. Especially Gen Z is constantly seeking for authentic, inclusive, and diverse brands as they are the first generation to choose brands based on authenticity. Especially the LGBTQ community’s representation in advertising is often perceived as inauthentic and superficial. Since Gen Z is not only a big consumer of fast fashion but also the first to include fast fashion as part of their everyday life, the fast fashion industry is required to be more authentic in its use of LGBTQ in advertising. Purpose: The purpose of this study is to explore how Gen Z perceives LGBTQ images in fast fashion advertising and how this impacts brand authenticity. Method: For this study, an exploratory research design with a qualitative approach was applied. Using an abductive approach, existing literature was used as a basis to create the conceptual model of this study. Further, a fictional fast fashion brand including five advertisements were created and presented to twenty informants during semi-structured interviews to gain a more in-depth understanding of the research problem. Conclusion: The study found that Gen Z’s perceptions of LGBTQ images in fast fashion advertising can be classified into three categories: positive, neutral, and negative perceptions. Informants with a positive perception perceived the brand to be authentic whilst informants with a negative perception the opposite. Since informants with a neutral perception sometimes had similar perceptions as the informants with a positive or negative perception, no clear answer on their perception of brand authenticity can be given.

This diploma thesis deals with the attitude of the Z generation to Czech documentary films and series. The aim of the work is to describe the common tendencies of the whole generation Z or its subgroups within their attitude to Czech documentary production. The research method for determining the attitude of this generational cohort is a questionnaire survey. In the beginning the Z generation is characterized, its formants and basic characteristics are analyzed. One of the subchapters also focuses especially on the Czech generation Z. In the theoretical part space is also devoted to documentary production, specifically its characteristics, typology and history of documents. The genre of the document is presented both in the global context and also in the Czech environment in the work. The practical part describes the research which has the form of a questionnaire survey. The results are presented for each evaluated question separately while at the end there is a collective summary with the most important and interesting findings from the research.

Background: In recent years, a new generation has rapidly entered the workforce and when this happens it is assumed that some level of disruption will come along. Since Generation Z have only been in the workforce for short amount of time, there is a lack of crucial research regarding their perceived experiences. Because different generations are assumed to have different values, a prominent challenge for organizations is how to correctly lead them. In other words, leadership preferences may differ when a new generation comes into play. Problem: As of today, there is a substantial knowledge gap regarding Generation Z preferred leadership styles among entry-level jobs. This knowledge gap can cause devastating effects for future organizations. Generation Z is a force to be reckoned with and shall soon become a prevailing member of the labor market in the near future. Purpose: The purpose of this study was to analyze the Swedish Generation Z preferred leadership styles, based on lived experiences in an entry-level job and to what extent they prefer transformational, transactional or laissez-faire leadership. The findings are expected to contribute to existing and new theoretical insights regarding Gen Z leadership preferences. Method: The research was conducted through seven qualitative semi-structured, open-ended interviews, which were analyzed using interpretive phenomenological analysis (IPA). Results: The findings described Generation Z ideal leader based on their thoughts and lived experiences. Gen Z prefers a leader that displays individual consideration, inspires followers and acts as a role model. These characteristics traits bare close resemblance of a transformational leader compared to transactional or laissez-fair leader. Acknowledging these results could contribute to a competitive advantage for organizations during their recruitment and development phase of Gen Z employees.

In the period 2005-2010 the Czech Republic has exhibited a growth in computer and Internet usage across society. As is to be expected from the literature, younger generations, especially what has been termed Generation Z, show significantly higher levels of computer literacy than older generations. Computer literacy is also at the highest level among the most highly educated and among households with children. Government policies to increase computer literacy have had positive effects, however they have only been a partial success. All schoolchildren have access to computers and the Internet, however there have been no effective policies for increasing computer literacy among the adult population. The result of this lack of policy is that the Czech Republic, in a position common to much of Europe, failed to meet the challenges of the Lisbon Strategy and will likely fail to meet the targets of Europe 2020.

Forskning visar att på grund av sociala mediers tillväxt har företag alltmer börjat synas på sociala medier i syfte att marknadsföra sina produkter genom så kallad influencer marketing. Tidigare forskning visar att sociala mediers utveckling i kombination med de ouppnåeliga idealen som influencers framställer har som konsekvens att många individers självkänsla och kroppsbild påverkas negativt. Därmed är uppsatsens syfte att undersöka hur influencers i generation Y påverkar unga kvinnor i generation Zs konsumtion samt självbild. Ytterligare har studien som intention att medföra kännedom om hur influencers upplevs från konsumentens perspektiv. I studien tillämpas en kvalitativ forskningsmetod med hjälp av 15 individuella semistrukturerade intervjuer med kvinnor i generation Z. Under kodning uppkom teman som kopplades samman med två teoretiska perspektiv, jämförelse och påverkan. Dessa perspektiv används för att analysera individers beteenden på sociala medier i relation till influencers. Resultatet visar att influencers generar ett stort engagemang bland kvinnor i generation Z. De unga kvinnor i generation Z som presenterades i studien påverkades negativt av influencers på sociala medier på så sätt att individer jämför sig med influencers ideal som anses vara ouppnåeliga. Det är av stor vikt att kunna relatera till influencers man följer för att öka trovärdigheten och övertygelsen. Att relatera till en influencer visade sig även vara en bidragande faktor till att man jämför sig, vilket framkom tydligt i empirin. Samtidigt visades jämförelse vara en övergång till att respondenter påverkas. Köpintentionen grundas i att influencers ses som inspiratörer när det kommer till mode. Genom rabattkoder upplever en del att de måste passa på och får en positiv attityd till spontanköp. Samtidigt känner en del individer köphets och att reklam upplevs opersonligt och blir snarare stressande än inspirerande. Studien bidrar till en ökad förståelse för både forskning och företag om konsekvenser som uppkommer vid användning av influencers samt en intention om hur influencers upplevs utifrån konsumentens perspektiv. Studien har begränsats till att undersöka hur unga kvinnor i generation Z upplever att de påverkas av influencers som exempelvis Bianca Ingrosso. Förslag till vidare forskning är att tillämpa ett företagsperspektiv då denna studien utgår från ett konsumentperspektiv. Ytterligare ett förslag är att undersöka generation Zs konsumentbeteende då det är den största generationen demografiskt. / Research shows that, due to the growth of social media, companies have increasingly begun to appear on social media in order to promote their products through so-called influencer marketing. Previous research shows that the development of social media in combination with the unreachable ideals of influencers has the consequence that many individuals' self-esteem and body image are adversely affected. The purpose of the essay is therefore to investigate how influencers in generation Y affect young women in generation Z's consumption and selfimage. Further, the study intends to bring awareness of how influencers are perceived from the consumer's perspective. The study uses a qualitative research method with the help of 15individual semi-structured interviews with women of generation Z. During coding, themes emerged that were linked to two theoretical perspectives, comparison and influence. These perspectives are used to analyze individuals' behaviors on social media in relation to influencers. The results show that influencers generate a high level of engagement among women of generation Z. The young women of generation Z presented in the study were adversely affected by influencers on social media in that individuals compare with influencers' ideals that are considered unreachable. It is of great importance to be able to relate to influencers you follow to increase their credibility and conviction. Relating to an influencer also proved to be a contributing factor in comparing oneself, which was evident in the empirical study. At the same time, comparison was shown to be a transition to the effect of respondents. The purchase intention is based on influencers being seen as inspirers when it comes to fashion. With discount codes, some people feel that they have to take care and get a positive attitude towards spontaneous purchases. At the same time, some individuals feel that buying and advertising are perceived as impersonal and rather stressful than inspiring. The study contributes to an increased understanding for both research and companies about the consequences that arise when using influencers and an intention about how influencers are experienced from the consumer's perspective. The study has been limited to examining how young women in generation Z feel that they are affected by influencers such as Bianca Ingrosso. Suggestions for further research are to apply a business perspective as this study is based on a consumer perspective. Another proposal is to examine Generation Z's consumer behavior as it is the largest generation demographically.

Hållbarhetsredovisningen kan ses som ett kommunikationsverktyg för företag gentemot sinaintressenter. Då konsumenter generellt sett är företagens primära inkomstkälla blir det därmed en viktig intressent för företaget. En konsumentgrupp som från och med i år beräknas vara den största konsumentgruppen och utgöra nästan 40% av världens konsumtion är Generation Z. Studiens syfte är att undersöka och förstå Generation Zs syn på två av Sveriges största fastfashion företag, nämligen H&M och Gina Tricot, hållbarhetsredovisningar utifrån 3Cprincipen.Vidare är syftet att undersöka om konsumentens attityd gentemot respektive fastfashion företag förändras efter att ha tagit del av hållbarhetsredovisningarna. Konsumenternas attityder analyserades utifrån Solomons et al. (2016) ABC-modell. Tio semistrukturerade intervjuer utfördes där deltagarna först fick dela med sig av generella åsikter kring företagen, därefter fick de ta del av hållbarhetsredovisningarna för att sedan dagen efter svara på ytterligare frågor. Resultatet visade på att konsumenter uppfattar respektivehållbarhetsredovisning som tydlig och jämförbar. För deltagarna som upplevde att hållbarhetsredovisningen var trovärdig var den genomgående anledningen till detta att den innehöll mer information. Konsumentens attityd gentemot respektive fast fashion företag förändrades inte ur många aspekter efter att ha tagit del av hållbarhetsredovisningen. Deltagarna som innan de tagit del av hållbarhetsredovisningen haft en positiv känsla gentemot företaget och därtill får en positiv känsla till hållbarhetsredovisningen uppgav däremot också ett förstärktbeteende. Med andra ord är de vara villiga att handla mer hos det företaget. Dock stämmer inte alltid attityd och beteende överens vilket innebär att man endast kan anta att de blir så. / The sustainability report can be seen as a communication tool for companies towards their stakeholders. Since consumers generally are seen as the company's primary source of income they therefore become an important stakeholder for the company. A consumer group that starting from this year is expected to be the biggest consumer group and make up for almost40% of the worlds consumption is Generation Z. This study is aimed to examine and understand Generation Z perception towards two of Sweden's biggest fast fashion companies, H&M and Gina Tricot, sustainability report based on the 3C-principle. Furthermore the purpose is to investigate if the consumers attitude towards respective fast fashion companies changes after they have taken part of the sustainability report. The consumers attitudes was analyzed based on Solomons et al. (2016) ABC-model. Ten semi-structured interviews were conducted where the participants first got to share their general opinions about the presented companies, thereafter they received the sustainability reports to then the day after answer additional questions. The results showed that the consumers perceive each sustainability report as clear and comparable. For the participants that perceived that the sustainability report as credible the frequent reason was that it contained more information. The consumers attitude towards the fast fashion companies did not change in many aspects after taking part of the sustainability report. The participants that had a previous positive feeling towards the company and in addition developed a positive feeling towards the sustainability report declared a reinforced behavior. However there is a gap between attitude and behavior and therefore one can only assume that they will behave that way. This paper is further on written in Swedish.