• tau particle flow
• parity
• tau
• Higgs
• hadronic tau
• CP
• charge conjugation
• 2HDM
• two-Higgs doublet models

The Higgs boson quantum numbers have been studied by the ATLAS and CMS collaborations after its discovery in 2012; alternative hypotheses to the Standard Model, concerning pure CP-eigenstate Higgs bosons, have been tested in the bosonic decay channels and excluded at more than 99.9% confidence level.
Nevertheless, the possibility still persists that the Higgs boson is an admixture of a CP-even and a CP-odd component, through a CP-mixing angle, as predicted by some extensions of the Standard Model (Two-Higgs Doublet Models for instance). Such a scenario would introduce CP violation in the Higgs sector, potentially helping to provide answers to some of the currently open questions in physics, such as the baryon asymmetry. The purpose of this thesis is to investigate the possibility of measuring the CP quantum numbers of the Higgs boson in its fermionic decays to pair of tau leptons, both decaying into hadrons. The tau reconstruction algorithm, called Tau Particle Flow, adopted by ATLAS at the beginning of the Run 2 is described and its performances are studied as a preliminary task. The Higgs CP analysis is carried out on the data collected by ATLAS in 2016 and the expected sensitivity to the mixing angle after a three-year run of High-Luminosity LHC is also provided, and estimated to be around 20 deg.