Studies of possible improvements to the b-Jet energy resolution applied to the search for the Higgs boson produced in association with a W boson at the ATLAS detector

Ravenscroft, Thomas Oliver (2015) Studies of possible improvements to the b-Jet energy resolution applied to the search for the Higgs boson produced in association with a W boson at the ATLAS detector. PhD thesis, University of Glasgow.

Abstract

This thesis presents a measurement of the cross-section for the produc- tion of a Higgs boson in association with a W boson. Where the Higgs boson decays to a pair of b-quarks and the W boson decays leptonically to a electron-neutrino pair or muon-neutrino pair. The measurements have been taken using 20 fb−1 of data collected at a centre-of-mass energy √s = 8 TeV from the ATLAS detector; one of the four main experiments at the Large Hadron Collider (LHC). An expected upper limit is calculated in the background-only hypothesis at 1.51 times the Standard Model expectation. The signal strength is measured at a Higgs boson mass m = 125 GeV to be μ = 3.22+0.71(stat.)+1.03(syst.)
H −0.69 −0.87
As part of the analysis performed, extensive studies have been
carried out into the impact of the four jet calibrations used by the WH → lνb ̄b analysis for the Run I result. Jet calibrations are used to correct for detector effects and inefficiencies in the reconstruction of the jets. In addition to the studies on the current jet calibration methods, two additional jet calibrations are studied and their perfor- mance within the analysis are measured, with comparisons against the nominal expected upper limit. The first additional calibration replaces the current jet pT calibration with one which uses different calibrations depending upon whether the jet contains a muon or not. By applying this calibration the expected upper limit improves to 1.50 times the Standard Model expectation.
The second calibration uses a regression to improve the b-jet resolu- tion. Using well modelled variables, there is no change in the expected upper limit, however by considering all variables, the expected upper limit improves to 1.47 times the Standard Model expectation, giving a 2.5% improvement to the nominal analysis.

• Item Type: Thesis (PhD)
• Qualification Level: Doctoral
• Subjects: Q Science > QC Physics
• Colleges/Schools: College of Science and Engineering > School of Physics and Astronomy
• Supervisor's Name: Britton, Professor David
• Date of Award: 2015
• Depositing User: Dr T Ravenscroft
• Unique ID: glathesis:2015-6664
• Copyright: Copyright of this thesis is held by the author.
• Date Deposited: 04 Sep 2015 07:21
• Last Modified: 10 Sep 2015 15:31
• URI: https://theses.gla.ac.uk/id/eprint/6664