Searches for Higgs boson pairs in the ATLAS experiment at the LHC to probe physics in and beyond the Standard Model

Project title: Searches for Higgs boson pairs in the ATLAS experiment at the LHC to probe physics in and beyond the Standard Model
Main applicant: Arnaud Ferrari, Division of High Energy Physics
Grant amount: 3 440 000 SEK for the period 2021-2024

The 2013 Nobel Prize in physics was awarded to F. Englert and P. Higgs for inventing a mechanism giving mass to all elementary particles, which was confirmed by the discovery of a Higgs boson (H) at CERN's Large Hadron Collider (LHC). This research project aims at further probing this mechanism, by establishing for the very first time the Higgs boson self-coupling through experimental searches for Higgs boson pairs (HH) in the proton–proton collision data to be recorded by the ATLAS experiment during the Run-3 of the LHC (2022-2024). In the Standard Model, the event rate for HH production is three orders of magnitude smaller than for single Higgs bosons, making the search channel of this research project very challenging. In turn, state-of-the-art detector technologies are needed to ensure that such rare events are recorded by ATLAS, and novel analysis techniques, based on advanced machine-learning and statistical tools, are essential to demonstrate the Higgs boson self-coupling. In the presence of new physics, HH event rates are likely to be enhanced. Also, new production modes and final states may become accessible. Searches for Higgs boson pairs therefore open a window towards physics beyond the Standard Model, including theories with extended Higgs sectors. In this inter-disciplinary project, collaboration with theorists is key to conduct phenomenological studies of new processes with spectacular signatures that may consist of not only two but even three Higgs bosons.