Higgs production in association with top quarks at the LHC

Kirby, Gavin (2016) Higgs production in association with top quarks at the LHC. PhD thesis, University of Glasgow.

Abstract

Since it has been found that the MadGraph Monte Carlo generator offers superior
flavour-matching capability as compared to Alpgen, the suitability of MadGraph
for the generation of ttb¯ ¯b events is explored, with a view to simulating this background
in searches for the Standard Model Higgs production and decay process
ttH, H ¯ → b
¯b. Comparisons are performed between the output of MadGraph and
that of Alpgen, showing that satisfactory agreement in their predictions can be
obtained with the appropriate generator settings.
A search for the Standard Model Higgs boson, produced in association with the top
quark and decaying into a b
¯b pair, using 20.3 fb−1
of 8 TeV collision data collected
in 2012 by the ATLAS experiment at CERN’s Large Hadron Collider, is presented.
The GlaNtp analysis framework, together with the RooFit package and associated
software, are used to obtain an expected 95% confidence-level limit of 4.2
+4.1
−2.0
times
the Standard Model expectation, and the corresponding observed limit is found to
be 5.9; this is within experimental uncertainty of the published result of the analysis
performed by the ATLAS collaboration.
A search for a heavy charged Higgs boson of mass mH± in the range
200 ≤ mH± /GeV ≤ 600, where the Higgs mediates the five-flavour beyond-theStandard-Model
physics process gb → tH± → ttb, with one top quark decaying leptonically
and the other decaying hadronically, is presented, using the 20.3 fb−1
8 TeV
ATLAS data set. Upper limits on the product of the production cross-section and
the branching ratio of the H± boson are computed for six mass points, and these
are found to be compatible within experimental uncertainty with those obtained by
the corresponding published ATLAS analysis.

• Item Type: Thesis (PhD)
• Qualification Level: Doctoral
• Keywords: science, experimental, particle, physics, data, analysis, Higgs, ATLAS, CERN, standard, model, supersymmetry, top, quark, BSM, MSSM, ttH, SUSY.
• Subjects: Q Science > QC Physics
• Colleges/Schools: College of Science and Engineering > School of Physics and Astronomy
• Supervisor's Name: Doyle, Professor A.T.
• Date of Award: 2016
• Depositing User: Mr Gavin Donald Kirby
• Unique ID: glathesis:2016-7550
• Copyright: Copyright of this thesis is held by the author.
• Date Deposited: 06 Oct 2016 10:16
• Last Modified: 21 Oct 2016 12:58
• URI: https://theses.gla.ac.uk/id/eprint/7550