Higgs boson production in the diphoton decay channel with CMS at the LHC: first measurement of the inclusive cross section in 13 TeV pp collisions, and study of the Higgs coupling to electroweak vector bosons

In this document two analyses of the properties of the Higgs boson in the diphoton decay channel with the CMS experiment at the LHC (Large Hadron Collider) are presented. The document starts with a theoretical introduction of the Standard Model and the Higgs boson physics, followed by a detailed description of the CMS detector. Then, photon reconstruction and identication algorithms are presented, with a particular focus on the dierences between the rst and the second run of the LHC, where the rst run (Run 1) took place from 2010 to 2012 with a centre-of-mass energy of 7 and then 8 TeV, while the second run (Run 2) started in 2015 with a centre-of-mass energy of 13 TeV. Per- formances of Run 1 and Run 2 reconstructions from the photon identication point of view are compared. Then the photon identication algorithm for the H → γγ analysis optimised for Run 2 is presented. To do that a multivariate analysis method is used. Performances of the photon identication at 13 TeV are nally studied and a data-simulation validation is performed. Afterwards, the H → γγ analysis using the rst Run 2 data is presented. The analysis is performed with a dataset corresponding to an integrated luminosity of 12.9 fb −1 . An event classication is performed to maximize signal signicance and to study specic Higgs boson production modes. The observed signicance for the Standard Model Higgs boson at m H σ signicance of 6.1 = 125.09 GeV is 5.6 is observed at m H σ , while 6.2 σ was expected, and the maximum = 126.0 GeV. Finally a feasibility study, having the aim of constraining the anomalous couplings of the Higgs boson to the vector bosons, is presented. This analysis is performed using the data collected at 8 TeV during Run 1 at the LHC, corresponding to an integrated luminosity of 19.7 fb −1 . This analysis exploits the production of the Higgs boson through vector boson fusion (VBF), with the Higgs decaying to 2 photons. The kinematic distributions of the di- jet system and the Higgs, which depend from the spin-parity hypothesis, are used to build some discriminants able to discriminate between dierent spin-parity hypotheses. These discriminants allow to dene dierent regions of the phase-space enriched with a certain spin-parity process. The Higgs boson signal yield is extracted in each region from a t to the diphoton mass, allowing to determine the contributions of the dierent processes and then constrain the production of a pseudo-scalar (spin-parity 0 − ) Higgs boson.