Properties of the Higgs-like state around 125 GeV in its decay into two photons at the CMS experiment
File(s)
Author(s)
Kenzie, Matthew
Type
Thesis
Abstract
Results are presented of a search for the Standard Model (SM) Higgs boson decaying into two photons at the Compact Muon Solenoid (CMS) experiment housed at the Large Hadron Collider (LHC), CERN. An excess of events is observed over the background expectation with a local significance of 5.7 (lower-case sigma), where the SM expectation is 5.2 (lower-case sigma), constituting a standalone discovery of the particle first observed by the ATLAS and CMS experiments in July 2012. Measurements of the particle's signal strength, mass and couplings are presented along with an analysis of its spin. The results show a high level of compatibility with the predictions for a SM Higgs boson. The observed state's signal strength relative to the SM expectation is found to be lower-case sigma/lower-case sigma_{\mathrm{SM}}=1.14^{+0.26}_{-0.23}$. The observed state's mass is found to be $124.72\pm 0.35$~GeV. The signal strength relative to the SM expectation when probing production mechanisms through fermionic modes only is 1.13^{+0.37}_{-0.31}, and from bosonic production modes only is 1.16^{+0.63}_{-0.57}. A spin-2 graviton, produced entirely by gluon fusion, is excluded at 94\%~C.L.~(92\% expected) and a spin-2 graviton, produced entirely by quark-antiquark annihilation, is excluded at 85\%~C.L.~(83\% expected).
Version
Open Access
Date Issued
2014-04
Date Awarded
2014-08
Copyright Statement
Attribution NoDerivatives 4.0 International Licence (CC BY-ND)
Advisor
Dauncey, Paul
Sponsor
Science and Technology Facilities Council (Great Britain)
Publisher Department
Physics
Publisher Institution
Imperial College London
Qualification Level
Doctoral
Qualification Name
Doctor of Philosophy (PhD)