CERN Accelerating science

Thesis
Report number	CERN-THESIS-2017-227
Title	Study of the Higgs boson properties in $H \to ZZ^* \to 4l$ decay channel with the ATLAS detector at LHC using data recorded at $\sqrt{s} = 8 - 13$ TeV
Author(s)	Mancini, Giada (Rome U., Tor Vergata)
Publication	220.
Thesis note	PhD : Rome U., Tor Vergata : 2017
Thesis supervisor(s)	Di Ciaccio, Anna ; Antonelli, Mario ; Di Nardo, Roberto
Note	Presented 15 Mar 2017
Subject category	Particle Physics - Experiment
Accelerator/Facility, Experiment	CERN LHC ; ATLAS
Abstract	The Higgs Boson is the keystone particle of the Standard Model (SM): its existence explains the massive nature of matter and makes the theory re-normalizable. The first measurements performed during the Run 1 at the Large Hadron Collider (LHC) allowed for the discovery of the Higgs boson with a mass around 125 GeV. Data recorded at $\sqrt{s}=7-8$ TeV have been used also to perform the first measurements of the Higgs boson properties, which have show that the 125 GeV resonance is consistent with a particle $J^P = 0^+$ (alternative hypotheses have been excluded with a $C.L.>95\%$) and its signal strength ($\mu = Ev_{obs}/Ev_{SM}$) and coupling measurements to vector bosons and fermions have been found to be consistent with the SM Higgs boson expectation with an accuracy of the order of 10$\%$. The increasing energy of the collisions and the increasing luminosity, resulting respectively in an enhancement of the Higgs boson production cross section (XS) and in improving the statistical power of the results, are being fundamental during Run 2 in order to improve the accuracy of such tests. This thesis's work concerns the measurements of the Higgs boson properties performed across Run 1 and Run 2 in the $H \to ZZ^* \to 4\ell$ decay channel with the ATLAS detector at the LHC. The inclusive and differential fiducial XS measurement (performed with 20.3 $fb ^{-1}$ at $\sqrt{s}=8$ TeV), the measurement of the XS per production mode and the coupling constants of the Higgs to SM particles, together with studies performed using Effective Field Theory (EFT) parameterizations (performed with 14.8 $fb ^{-1}$ at $\sqrt{s}=13$ TeV), are extensively studied and discussed in this thesis.

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