Cross-section measurement of Higgs Boson production in association with a Z boson, decaying via WW*, using the ATLAS detector at the LHC at √ s = 13.6 TeV

Abstract

The Higgs boson discovery in 2012 by the ATLAS and CMS experiments at the LargeHadron Collider at CERN made the Standard Model (SM) predictions complete. However, the Standard Model also comes with its own flaws, it does not explain phenomenon like matter-antimatter asymmetry and existence of dark matter and dark energy in the universe. Studying the properties of existing Standard Model particles helps us to better understand their limitations. Higgs boson is responsible in providing masses to other fundamental particles via Higgs Mechanism and Yukawa couplings. Studying the various production and decay modes of Higgs boson will help us understand the interactions of these fundamental particles precisely. In this thesis, Higgs boson production in association with a Z boson and its decay via WW∗ channel into a fully leptonic final state is discussed. The data collected during Run 3 of the ATLAS detector from 2022 and 2023 is used. Since this signal process is limited by statistics, advanced machine learning algorithms, in particular, deep neural networks have been deployed to discriminate between signal and any background processes affecting this analysis. Results obtained from statistical treatment using the maximum likelihood estimator show potential discovery when combining the results with the V H analysis in Run 2+3. Prospects are also discussed which will help achieve the discovery potential and make cross-section measurements in the transverse momentum bins of Z boson.