Probing new physics with boosted $H \rightarrow b\bar{b}$ decays with the ATLAS detector at 13 TeV

The discovery of the Higgs boson by the ATLAS and CMS collaborations at the Large Hadron Collider was a major success in particle physics. Even though studies of the Higgs boson suggest that its properties are in agreement with the Standard Model (SM) expectations, there are still many open questions connected to the physics of the Higgs sector. New physics extensions of the SM attempt to answer these questions. Many new physics models predict heavy resonances which decay into final states with a SM Higgs boson. In this thesis a search for a heavy resonance $V^{\prime}$ decaying via a $W$ or $Z$ boson and a Higgs boson into a final state with leptons and $b$-quark jets with the ATLAS detector is presented. One of the main challenges in this analysis is the reconstruction of Higgs bosons with a high Lorentz-boost decaying into $b$-quark jets. In this thesis, reconstruction algorithms for boosted $H\rightarrow b\bar{b}$ decays are discussed, laying emphasis on the identification of $b$-jets ($b$-tagging) in boosted topologies. A new method for a data-based double-$b$-tagging calibration using gluon splitting ($g\rightarrow b\bar{b}$) events is presented for the first time for the ATLAS experiment.