PROBING THE HIGGS BOSON WITH THE ATLAS DETECTOR: PRECISION MEASUREMENTS OF THE MASS AND SEARCH FOR RARE DECAYS TO A LOW-MASS DILEPTON SYSTEM AND A PHOTON IN PROTON-PROTON COLLISIONS AT THE LHC
type: CreativeWork
description: This thesis presents three analyses based on proton--proton collision data recorded by the ATLAS detector at the Large Hadron Collider, using the full Run~2 dataset collected between 2015 and 2018 at a centre-of-mass energy of $\sqrt{s} = 13$~TeV, corresponding to an integrated luminosity of 140~fb$^{-1}$, and data recorded during the first part of Run~3 between 2022 and 2024 at $\sqrt{s} = 13.6$~TeV, corresponding to 165~fb$^{-1}$. The analyses focus on a detailed investigation of the Higgs boson within the Standard Model (SM), through the precision measurement of one of its fundamental parameters, the Higgs boson mass $m_H$, and the search for a rare SM decay mode not yet observed, namely the decay into a low-mass dilepton system and a photon. \noindent The first analysis presents a precision measurement of the Higgs boson mass in the diphoton decay channel, $H \rightarrow \gamma\gamma$, using the full Run~2 dataset. The Higgs boson mass is measured to be $m_H = 125.17 \pm 0.11\,(\mathrm{stat.}) \pm 0.09\,(\mathrm{syst.})~\mathrm{GeV} = 125.17 \pm 0.14~\mathrm{GeV}$. The improved precision with respect to previous measurements is driven by the larger dataset and by significant advances in the calibration of the photon energy response, resulting in a measurement that is now statistically limited. A combination with the corresponding Run~1 measurement yields $m_H = 125.22 \pm 0.14~\mathrm{GeV}$. \noindent The second analysis furthermore combines the Higgs boson mass measurements obtained in the $H \rightarrow \gamma\gamma$ and $H \rightarrow ZZ^* \rightarrow 4\ell$ decay channels using ATLAS Run~1 and Run~2 data. The combined result, $m_H = 125.11 \pm 0.09\,(\mathrm{stat.}) \pm 0.06\,(\mathrm{syst.})~\mathrm{GeV} = 125.11 \pm 0.11~\mathrm{GeV}$, achieves a relative precision of 0.9 per mille and represents the most precise determination of the Higgs boson mass to date. All mass measurements are found to be consistent with each other and with previous ATLAS and CMS r…
abstract: This thesis presents three analyses based on proton--proton collision data recorded by the ATLAS detector at the Large Hadron Collider, using the full Run~2 dataset collected between 2015 and 2018 at a centre-of-mass energy of $\sqrt{s} = 13$~TeV, corresponding to an integrated luminosity of 140~fb$^{-1}$, and data recorded during the first part of Run~3 between 2022 and 2024 at $\sqrt{s} = 13.6$~TeV, corresponding to 165~fb$^{-1}$. The analyses focus on a detailed investigation of the Higgs boson within the Standard Model (SM), through the precision measurement of one of its fundamental parameters, the Higgs boson mass $m_H$, and the search for a rare SM decay mode not yet observed, namely the decay into a low-mass dilepton system and a photon. \noindent The first analysis presents a precision measurement of the Higgs boson mass in the diphoton decay channel, $H \rightarrow \gamma\gamma$, using the full Run~2 dataset. The Higgs boson mass is measured to be $m_H = 125.17 \pm 0.11\,(\mathrm{stat.}) \pm 0.09\,(\mathrm{syst.})~\mathrm{GeV} = 125.17 \pm 0.14~\mathrm{GeV}$. The improved precision with respect to previous measurements is driven by the larger dataset and by significant advances in the calibration of the photon energy response, resulting in a measurement that is now statistically limited. A combination with the corresponding Run~1 measurement yields $m_H = 125.22 \pm 0.14~\mathrm{GeV}$. \noindent The second analysis furthermore combines the Higgs boson mass measurements obtained in the $H \rightarrow \gamma\gamma$ and $H \rightarrow ZZ^* \rightarrow 4\ell$ decay channels using ATLAS Run~1 and Run~2 data. The combined result, $m_H = 125.11 \pm 0.09\,(\mathrm{stat.}) \pm 0.06\,(\mathrm{syst.})~\mathrm{GeV} = 125.11 \pm 0.11~\mathrm{GeV}$, achieves a relative precision of 0.9 per mille and represents the most precise determination of the Higgs boson mass to date. All mass measurements are found to be consistent with each other and with previous ATLAS and CMS r…
author: NASELLA, LAURA
language: eng
keywords: Particle physic, Higgs physic, Collider experiment, Particle detector, Standard Model, Settore PHYS-01/A - Fisica sperimentale delle interazioni fondamentali e applicazioni
date published: 2026-03-25
date modified: 2026-07-27T20:18:51Z
provider: Università degli Studi di Milano
publisher: Networked Digital Library of Theses and Dissertations
type: WebPage
source organization: Università degli Studi di Milano

PropertyValue
property ID: Handle
value: https://hdl.handle.net/2434/1225332