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Searches for neutral Higgs bosons decaying to tau pairs and measurement of the Z+b-jet cross section with the CMS detector

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Title: Searches for neutral Higgs bosons decaying to tau pairs and measurement of the Z+b-jet cross section with the CMS detector
Authors: Gilbert, Andrew
Item Type: Thesis or dissertation
Abstract: The Compact Muon Solenoid (CMS) is a general-purpose particle detector at the CERN Large Hadron Collider. It is designed to search for the Higgs boson and evidence of new physics and to test the predictions of the standard model (SM) at the TeV scale. This thesis describes analyses of proton-proton collision data recorded by CMS during 2011 and 2012. A study of Z boson production in association with b jets, using 2.1 fb^{-1} of data recorded at a centre-of-mass energy of 7 TeV, is presented. The cross sections for production with exactly one, or at least two, b jets are measured, and the event kinematics are compared to the predictions of the madgraph event generator interfaced with pythia for hadronisation and parton showering. Searches for neutral Higgs bosons decaying to tau pairs are also presented. One search is in the context of the SM Higgs boson, for mass hypotheses in the range 90-150 GeV, and the other in the minimal supersymmetric standard model (MSSM), in which three neutral Higgs bosons are predicted and the search range is from 90 GeV to 1 TeV. Both searches use 4.9 fb-1 of data collected at 7 TeV and 19.7 fb^{-1} collected at 8 TeV. In the SM search an excess of events above the background expectation is observed and found to be compatible with the SM expectation for the 125 GeV Higgs boson. The observed (expected) local significance of this excess is 3.0 (3.1) standard deviations at 125 GeV. No significant excess is observed in the MSSM search. Upper limits at the 95% confidence level are determined, both in the m_A-tan(beta) parameter space of the m_h^max scenario and on the production cross sections in a model-independent interpretation.
Content Version: Open Access
Issue Date: May-2014
Date Awarded: Sep-2014
URI: http://hdl.handle.net/10044/1/23290
DOI: https://doi.org/10.25560/23290
Supervisor: Colling, David
Sponsor/Funder: Science and Technology Facilities Council (Great Britain)
Department: Physics
Publisher: Imperial College London
Qualification Level: Doctoral
Qualification Name: Doctor of Philosophy (PhD)
Appears in Collections:Physics PhD theses

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