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Title: Search for a Higgs Boson in the H->ZZ and ZH->ll+invisible channels with the ATLAS detector
Author: Price, Joseph
Awarding Body: University of Liverpool
Current Institution: University of Liverpool
Date of Award: 2013
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A pre-data sensitivity study to search for a high mass Standard Model (SM) Higgs (m_H = 200 GeV) in ATLAS using the H -> ZZ -> llll channel is presented. It is found that it would be possible to exclude a SM Higgs in part of this high mass region with limited luminosity. Using this channel a search at the LHC for the SM Higgs boson in the first ~40 inverse picobarns of data was conducted and is presented in this thesis, along with the results from the H->ZZ->llvv and H->ZZ->llqq channels using a similar dataset. It is found that the channel with the best sensitivity to a SM Higgs with mass greater than 200 GeV is the H->ZZ->llll channel. A search for the SM Higgs boson using the H->ZZ->llvv channel is presented, using 4.7 inverse femtobarns of data at a centre-of-mass energy of s = 7 TeV. A Higgs boson with a mass between 320 and 560 GeV is excluded at a 95\% confidence level using this channel alone. This analysis was published in 2011 and updated in 2012, and results from this search are used in the ATLAS paper, describing the discovery of a new Higgs-like boson with ~m_H = 125 GeV. Finally a direct search is performed for anomalous invisible decays of the Higgs boson candidate at ~125 GeV using both the 2011 dataset and the 2012 dataset at centre-of-mass energy s = 7 and 8 TeV respectively. An upper limit of 65% is set on the allowed H->inv branching fraction at 95% confidence level. Additional searches are performed using the same dataset on further invisibly decaying Higgs-like bosons at masses between 115 and 300 GeV. No excess is observed. This analysis was published as a preliminary result in March 2013, and a paper using the full 2011 and 2012 datasets is scheduled to be published in the summer of 2013.
Supervisor: Vossebeld, Joost Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available