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Title: Differential cross section measurements in H→ WW and prospects of observing H→ bb in future LHC runs at the ATLAS detector
Author: Glaysher, Paul Christopher Frederick
ISNI:       0000 0004 6351 8165
Awarding Body: University of Edinburgh
Current Institution: University of Edinburgh
Date of Award: 2016
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The highly celebrated discovery of a new particle with a mass of 125 GeV in proton-proton collisions by the ATLAS and CMS experiments at the CERN Large Hadron Collider in 2012 has been shown to be compatible with the Standard Model description of the Higgs boson. However, in order to fully verify the Standard Model nature of the Higgs boson, most of its properties still remain to be measured. Such measurements include differential cross section measurements, which are shown here for the H→WW decay channel and the coupling of the Higgs boson to bottom quarks, for which a study of future prospects is presented. Differential fiducial cross section measurements of the Higgs boson were performed in the H → WW*→lvlv channel at the ATLAS detector with 20 fb−1 of √s = 8 TeV collision data. For Higgs bosons produced by gluon-gluon fusion, the cross section is measured as a function of kinematic variables, including transverse momentum and rapidity of the Higgs boson, as well as the number of jets associated with the Higgs event. The obtained distributions are unfolded to a fiducial volume using a two-dimensional iterative Bayesian algorithm. The measured fiducial differential cross sections are compared to predictions from Monte Carlo generators. The total cross section measured in the fiducial volume defined by the charged lepton and neutrino kinematic properties is 36.0 ± 9.7 fb. Additionally the jet-veto efficiency in the fiducial volume is extracted from the differential cross sections. An analysis is presented of Higgs boson production and decay into bottom quarks in association with a vector boson at the ATLAS detector for the future high-luminosity LHC with proton-proton collisions at √s = 14 TeV. The vector bosons are reconstructed from Z→l+l− or W→lv final states, where l is an electron or muon. The analysis uses generator-level Monte Carlo samples to which efficiency and resolution smearing functions are applied. These reproduce the expected resolution of the upgraded ATLAS detector for the foreseen amount of pile-up due to multiple overlapping proton-proton collisions. The analysis of the ZH(→ l+l−b¯b) channel is presented and results are combined with the WH(→lvb¯b) channel from a corresponding study. For an integrated luminosity of 300 fb−1 using an average pile-up of 60, the expected significance is 3.9 σ with an expected error on the signal strength of 25%. Likewise, for 3000 fb−1 using an average pileup of 140 the expected significance is 8.8 σ , and the error on the signal strength is expected to be about 15%.
Supervisor: Martin, Victoria ; Clark, Philip Sponsor: Science and Technology Facilities Council (STFC)
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available
Keywords: LHC ; Large Hadron Collider ; Higgs boson ; ATLAS