CERN Accelerating science

Thesis
Report number	CERN-THESIS-2015-414
Title	A search for the ttH (H → bb) channel at the Large Hadron Collider with the ATLAS detector using a matrix element method
Author(s)	Basye, Austin Thomas (Illinois U., Urbana)
Publication	235.
Thesis note	PhD : Illinois U., Urbana : 2015-07-07
Thesis supervisor(s)	Liss, Tony
Note	Presented on 2015-05-20
Subject category	Particle Physics - Experiment
Accelerator/Facility, Experiment	CERN LHC ; ATLAS
Abstract	A matrix element method analysis of the Standard Model Higgs boson, produced in association with two top quarks decaying to the lepton-plus-jets channel is presented. Based on 20.3 fb−1 of √s=8 TeV data, produced at the Large Hadron Collider and collected by the ATLAS detector, this analysis utilizes multiple advanced techniques to search for tt ̄H signatures with a 125 GeV Higgs boson decaying to two b-quarks. After categorizing selected events based on their jet and b-tag multiplicities, signal rich regions are analyzed using the matrix element method. Resulting variables are then propagated to two parallel multivariate analyses utilizing Neural Networks and Boosted Decision Trees respectively. As no significant excess is found, an observed (expected) limit of 3.4 (2.2) times the Standard Model cross-section is determined at 95% confidence, using the CLs method, for the Neural Network analysis. For the Boosted Decision Tree analysis, an observed (expected) limit of 5.2 (2.7) times the Standard Model cross-section is determined at 95% confidence, using the CLs method. Corresponding unconstrained fits of the Higgs boson signal strength to the observed data result in the measured signal cross-section to Standard Model cross-section prediction of μ = 1.2 ± 1.3(total) ± 0.7(stat.) for the Neural Network analysis, and μ = 2.9 ± 1.4(total) ± 0.8(stat.) for the Boosted Decision Tree analysis.

Corresponding record in: Inspire