A search for the ttH (H → bb) channel at the Large Hadron Collider with the ATLAS detector using a matrix element method

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.

Name thesis:degree_name

Ph.D.

Level thesis:degree_level

Dissertation

Discipline thesis:degree_discipline

Physics

Grantor

University of Illinois at Urbana-Champaign

Year dc:date

2015

Author dc:creator

• Basye, Austin Thomas

Contributors dc:contributor

• Liss, Tony M.
• El-Khadra, Aida X
• Eckstein, James N.
• Martinez Outschoorn, Verena I

• Higgs Boson
• Large Hadron Collider (LHC)
• A Toroidal LHC Apparatus (ATLAS)
• 8 trillion electron volt (TeV)
• ttH
• H to bb
• Matrix Element Method
• Neural Network
• Boosted Decision Tree
• Standard Model

Statement dc:rights

• Copyright 2015 Austin T. Basye

Language dc:language

en

Handle dc:identifier

http://hdl.handle.net/2142/88000

OAI identifier oai:identifier

oai:www.ideals.illinois.edu:2142/88000