Date of Award

2015

Degree Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Graduate Group

Physics & Astronomy

First Advisor

Ira J. Kroll

Abstract

This thesis presents preliminary results of a search for Higgs boson production

in association with top quarks in multilepton final states. The search

was conducted in the 2012 dataset of proton-proton

collisions delivered by the CERN Large Hadron Collider at a center-of-mass energy of 8 TeV and collected by

the ATLAS experiment. The dataset corresponds to an integrated luminosity of

20.3 inverse femtobarns. The analysis is conducted by measuring event counts in

signal regions distinguished by the number of leptons (2 same-sign,

3, and 4), jets and b-tagged jets present in the reconstructed events. The observed

events in the signal regions constitute an excess over

the expected number of background events. The results

are evaluated using a frequentist statistical model.

The observed exclusion upper limit at the 95 % confidence

level is 5.50 times the predicted Standard Model production cross section for Higgs production in association with top quarks. The fitted value of the ratio of the observed production rate to the expected Standard Model

production rate is 2.83 $+$ 1.58 $-$ 1.35.

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