Measurement of the H→WW*→lvlv decay using same-flavour leptons in pp collisions at √s = 13 TeV with the ATLAS detector

Higgs boson production via gluon-gluon fusion and vector-boson fusion in the $\textit{H} \rightarrow \textit{WW*} \rightarrow l\nu l\nu$ decay mode is measured in the same-flavour channel, where the two leptons are either both electrons or both muons. The proton-proton collision data used in this analysis were produced at the Large Hadron Collider with a centre-of-mass energy of 13 TeV and recorded by the ATLAS detector between 2015 and 2018, corresponding to an integrated luminosity of 139 fb$^{-1}$. This thesis utilizes the traditional cut-based approach, which involves defining event selection criteria purely based on kinematic or geometric observables. The goal of this analysis is to measure the total cross-sections of the gluon-gluon fusion and vector-boson fusion Higgs production modes and compare them to the values predicted by the Standard Model

ATLAS Run 2 searches for electroweak production of supersymmetric particles interpreted within the pMSSM

A summary of the constraints from searches performed by the ATLAS collaboration for the electroweak production of charginos and neutralinos is presented. Results from eight separate ATLAS searches are considered, each using 140 fb−1 of proton-proton data at a centre-of-mass energy of √ = 13 TeV collected at the Large Hadron Collider during its second data-taking run. The results are interpreted in the context of the 19-parameter phenomenological minimal supersymmetric standard model, where R-parity conservation is assumed and the lightest supersymmetric particle is assumed to be the lightest neutralino. Constraints from previous electroweak, flavour and dark matter related measurements are also considered. The results are presented in terms of constraints on supersymmetric particle masses and are compared with limits from simplified models. Also shown is the impact of ATLAS searches on parameters such as the dark matter relic density and the spin-dependent and spin-independent scattering cross-sections targeted by direct dark matter detection experiments. The Higgs boson and Z boson ‘funnel regions’, where a low-mass neutralino would not oversaturate the dark matter relic abundance, are almost completely excluded by the considered constraints. Example spectra for non-excluded supersymmetric models with light charginos and neutralinos are also presented

Constraints on the Higgs boson self-coupling from single- and double-Higgs production with the ATLAS detector using pp collisions at √s=13 TeV

Constraints on the Higgs boson self-coupling are set by combining double-Higgs boson analyses in the bb̅bb̅, bb̅τ+τ− and bb̅γγ decay channels with single-Higgs boson analyses targeting the γγ, ZZ∗, WW∗, τ+τ− and bb̅ decay channels. The data used in these analyses were recorded by the ATLAS detector at the LHC in proton–proton collisions at √s = 13 TeV and correspond to an integrated luminosity of 126–139 fb−1. The combination of the double-Higgs analyses sets an upper limit of μHH <2.4 at 95% confidence level on the double-Higgs production cross-section normalised to its Standard Model prediction. Combining the single-Higgs and double-Higgs analyses, with the assumption that new physics affects only the Higgs boson self-coupling (λHHH ), values outside the interval −0.4 < κλ = (λHHH /λSMHHH) < 6.3 are excluded at 95% confidence level. The combined single-Higgs and double-Higgs analyses provide results with fewer assumptions, by adding in the fit more coupling modifiers introduced to account for the Higgs boson interactions with the other Standard Model particles. In this relaxed scenario, the constraint becomes −1.4 < κλ < 6.1 at 95% CL

ATLAS flavour-tagging algorithms for the LHC Run 2 pp collision dataset

The flavour-tagging algorithms developed by the ATLAS Collaboration and used to analyse its dataset of √s = 13 TeV pp collisions from Run 2 of the Large Hadron Collider are presented. These new tagging algorithms are based on recurrent and deep neural networks, and their performance is evaluated in simulated collision events. These developments yield considerable improvements over previous jet-flavour identification strategies. At the 77% b-jet identification efficiency operating point, light-jet (charm-jet) rejection factors of 170 (5) are achieved in a sample of simulated Standard Model tt¯ events; similarly, at a c-jet identification efficiency of 30%, a light-jet (b-jet) rejection factor of 70 (9) is obtained

Measurement of the H→WW∗→lνlνH \rightarrow WW^{*} \rightarrow l\nu l\nu decay using same-flavour leptons in pp\textit{pp} collisions at s\sqrt{s} = 13 TeV with the ATLAS detector

Higgs boson production via gluon-gluon fusion and vector-boson fusion in the $\textit{H} \rightarrow \textit{WW*} \rightarrow l\nu l\nu$ decay mode is measured in the same-flavour channel, where the two leptons are either both electrons or both muons. The proton-proton collision data used in this analysis were produced at the Large Hadron Collider with a centre-of-mass energy of 13 TeV and recorded by the ATLAS detector between 2015 and 2018, corresponding to an integrated luminosity of 139 fb$^{-1}$. This thesis utilizes the traditional cut-based approach, which involves defining event selection criteria purely based on kinematic or geometric observables. The goal of this analysis is to measure the total cross-sections of the gluon-gluon fusion and vector-boson fusion Higgs production modes and compare them to the values predicted by the Standard Model