Self-interacting Higgs bosons - Searching for di-Higgs production with the ATLAS detector
Alessio Pizzini is a PhD student in the department Energy, Materials and Systems. Promotors are promotors are prof. T.A. du Pree from the faculty of Science & Technology and prof.dr. P. Ferrari from the Radboud University Nijmegen.
In 2012 the Higgs boson was discovered by the ATLAS and CMS collaborations at the Large Hadron Collider (LHC) at CERN. This discovery marked a significant milestone in particle physics, as the Higgs boson, the final particle of the Standard Model (SM) to be experimentally found, solidified the SM as one of the most successful theories in the history of physics, having resisted decades of attempts of falsification.
However, the discovery of this new particle was only the first step of its characterization, as the confirmation of the Higgs mechanism requires the determination of its quantum numbers, widths and couplings. Playing such a key role in the architecture of the SM, it is a topic of the utmost importance in understanding and validating the SM, as well as a promising portal to physics beyond the SM. More specifically, studying the properties of the Higgs boson can allow us to test the Brout-Englert-Higgs mechanism and hence the whole electro-weak symmetry breaking mechanism, which is one of the main goals of the LHC.
Among the most elusive and yet insightful of these properties are the trilinear and quadrilinear couplings, i.e. the parameters describing the interaction a Higgs boson is expected to experience with other Higgs bosons. Experimentally, these interactions (namely the trilinear Higgs coupling) manifest themselves in di-Higgs production, a rare process resulting in the creation of two Higgs bosons at the same time. This thesis describes a search for di-Higgs production in the final state with two b-quarks and two charged leptons, performed on the data collected by the ATLAS experiment during the LHC's second run throughout 2015 to 2018, corresponding to an integrated luminosity of 140 inverse femtobarn. The search targets non-resonant production only.
The selection is optimized for cases where one of the Higgs bosons decays via the H -> bb channel and the other via the dileptonic modes of the H -> WW* / ZZ* / tau tau channels. Moreover, while the previous iteration of this analysis was only targeting the largest di-Higgs production mode, gluon-gluon fusion (ggF), the analysis presented in this thesis presents a category dedicated to the second-largest di-Higgs production mode, Vector Boson Fusion (VBF).
