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Title: Study of Higgs boson production through its decay to two photons using data collected at a centre-of-mass energy of 13 TeV with the CMS detector
Author: Corpe, Louie
ISNI:       0000 0004 6423 7285
Awarding Body: Imperial College London
Current Institution: Imperial College London
Date of Award: 2017
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A study of $H \rightarrow \gamma \gamma$ with 12.9 fb$^{-1}$ of data from p-p collisions at $\sqrt{s}=13$ TeV is presented. The data were collected at the start of LHC Run 2 by the CMS experiment between April and July 2016. The result is a new standalone observation of the Higgs boson in the diphoton decay channel. The significance of the excess is observed to be $5.7\sigma$ ($6.3\sigma$ expected) at the combined Run 1 best-fit Higgs boson mass of $m_{H}=125.09$ GeV. The maximum significance of $6.1\sigma$ ($6.3\sigma$ expected) is observed at $m_{H}=125.09$ GeV. The measured Higgs boson signal strength is $\hat{\mu} = 0.89^{+0.20}_{-0.17} = 0.89 \pm 0.15 {~(stat.)~} ^{+0.09}_{-0.06} {~(syst.)~} ^{+0.07}_{-0.05} {~(theo.)}$. The signal strength is measured separately for: fermionic and bosonic production modes, giving $ \hat{\mu}_{{VBF},{VH}} = 1.00^{+0.10}_{-0.10}$ and $\hat{\mu}_{{ggH},{ttH}} = 1.00^{+0.10}_{-0.10}$; and for the ggH, VBF and ttH production modes, giving $\hat{\mu}_{{ggH}} = 0.73^{+0.24}_{-0.22}$, $\hat{\mu}_{{VBF}} = 1.45^{+0.8}_{-0.7}$, and $\hat{\mu}_{{ttH}} = 1.75^{+1.4}_{-1.1}$. Measurements of the Higgs boson coupling modifiers yield $\hat{\kappa}_{{f}} = 0.66^{+0.43}_{-0.22}$, $\hat{\kappa}_{{V}} = 0.90^{+0.10}_{-0.10}$ for the fermionic and bosonic coupling modifiers and $\hat{\kappa}_{g} = 0.66^{+0.27}_{-0.19}$, $\hat{\kappa}_{\gamma} = 1.23^{+0.24}_{-0.26}$ for the gluon and photon effective coupling modifiers. All measurements are found to be consistent with the theoretical expectation for a SM-like Higgs boson.
Supervisor: Dauncey, Paul ; Seez, Christopher Sponsor: Science and Technology Facilities Council
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral