Probing the ground state of the Universe with Higgs boson pairs

The main objective of this project is to use data from the ATLAS experiment at CERN’s Large Hadron Collider (LHC) to measure the Higgs self-coupling parameter and thereby explore the shape of the Higgs potential.

This shape controls the dynamics of the electroweak phase transition which occurred a picosecond after the Big Bang, leading to electroweak symmetry breaking and the generation of elementary particle masses.

The nature of the phase transition can have large cosmological implications, e.g. a first order phase transition is required to generate the observed matter-antimatter asymmetry. At the LHC, the Higgs self-coupling parameter is best measured via Higgs boson pair production (HH). Assuming the cross section predicted by the Standard Model (SM), observation of HH is expected in the 2030s.

But as many extensions of the SM predict enhanced HH production rates and modified kinematic distributions, an observation could occur even in the upcoming Run 3 of the LHC (2022-2026).

In this project I will search for contributions from physics beyond the SM to HH production using effective field theories.

I will also improve future searches by exploiting the capabilities of the new tracking and timing detectors to be installed in ATLAS after Run 3.

At the end of the project, the result will either be an observation of BSM contributions to HH production or, in the case of a null-result, improved limits on parameters constraining such contributions by more than a factor of two.