Testing the Standard Model with precision flavour measurements at the ATLAS experiment

ATLAS is one of the main experiments at the Large Hadron Collider (LHC) located at CERN in Switzerland. Over thirteen years, ATLAS has achieved significant results, including the discovery of the Higgs boson in 2012. However, the Standard Model remains an active area of research. In this context, recognising the flavour of quarks plays a crucial role in identifying interesting processes. This thesis focuses on measuring the W boson produced in association with a charm quark. In this analysis, determining the flavour of both the charm and strange quarks in the proton—responsible for the production of the W boson and charm—is fundamental for measuring the cross-section and improving the precision of the strange quark distribution function. This thesis will present all the analytical techniques developed for measuring this process, along with the results for both the differential and total cross-sections, including their statistical and systematic uncertainties. The second part of the work addresses the challenge of distinguishing a color singlet, such as the Higgs boson, from another configuration, such as a gluon, by employing color-sensitive variables, starting with the identification of the flavour of two b-quarks. This thesis will also present promising results that have been published in a research article.