Feasibility study for inclusive measurements of Higgs branching ratios to hadronic final states with the ATLAS detector

Abstract

The investigation of the decay properties of the Higgs boson is an important part of the LHC physics programme. An accurate determination of the decay branching ratios to the hadronic states bb, cc, gg is necessary for studying the Higgs couplings and thus clarifying the understanding of the particle mass generation mechanism and validating the predictions of the Standard Model. At the same time, possible deviations from these values could indicate the existence of new physics. Identifying hadronic states is based on flavour tagging jets and as current methods are able to mostly identify well b-jets, the branching ratio of the Higgs boson to charm quarks has not been measured. This work studies the feasibility of doing an inclusive measurement of the Higgs hadronic branching ratios. The attempt at determining all three of them simultaneously is based on di-jet discriminants created using the response of a flavour tagging algorithm. For this to be possible, it's necessary to first extract the contribution from background processes attributed to the strong interaction. Thus, the flavour composition of the background is studied and a methodology for estimating it in the signal region is developed. This thesis shows that with the present flavour tagging accuracy, the branching ratios cannot be determined. Therefore, modifications to the output of the flavour tagging algorithm are examined. The study demonstrates the required level of efficiency and mistagging rate of flavour tagging for enabling the analysis with the goal to motivate further enhancements in the discrimination between b-, c- and light-flavour jets.