Thesis title: Indirect on-shell constraint on the Higgs boson width via signal–background interference in the diphoton channel at CMS
The Standard Model Higgs boson with a mass of 125 GeV is predicted to have a
decay width of 4.1 MeV. Direct measurements of the Higgs width using on-shell
Higgs boson production are limited by the experimental resolution, which is about 1
GeV in the diphoton and four-lepton final states. This thesis presents a constraint
on the Higgs boson width obtained from the diphoton invariant mass distribution
in on-shell Higgs decays, using the interference between the amplitudes of the
gluon-gluon fusion to Higgs resonance, with subsequent diphoton decay, and the
continuum QCD gluon-gluon to diphoton process. The study was performed using
proton-proton collision data at a center-of-mass energy of 13 TeV, collected by the
CMS experiment during LHC Run 2, corresponding to an integrated luminosity of
137 inverse femtobarns. The observed (expected) upper limit on the Higgs boson
width is 92 MeV (138 MeV) at the 95% confidence level.