Identification of boosted Higgs bosons for new physics searches and improvement of the ATLAS tracker for the high luminosity phase of LHC

This thesis covers the main contributions of the author during the PhD program: the in-situ calibration of the $X \rightarrow b\bar{b}$ tagger using $Z$+jets events, the measurement of the $V(\rightarrow qq')H(\rightarrow b)\bar{b}$ production at high transverse momentum and the characterisation of the planar pixel modules for the ATLAS Inner Tracker (ITk) upgrade of the inner detector and future colliders.