Thesis proposal CSC 2020

This thesis is reserved for Chinese students applying in the context of the China Scholarship Council programme.

After the discovery of the Higgs boson by ATLAS and CMS at CERN during the Large Hadron Collider (LHC) Run 1 and the measurement of many of its properties and the observation of its couplings to several particles with Run 2 data, the coupling of the Higgs boson to the elementary fermions of the second generation is still not established. This is one of the main goals of the LHC Run 3, through the search for the rare (and yet unobserved) Higgs boson decays to muon pairs. The goal of this thesis is to perform the search for the Higgs to dimuon decay with the full ATLAS Run 3 data, and, in combination with previous data, to obtain the first evidence of such decay and verify if the observed branching ratio is in good agreement with the standard model prediction. In addition, the student will search for the decay to a Z boson and a photon, another Higgs boson decay predicted by the Standard Model of particle physics but not observed yet, which could shed light on the possible compositeness of the Higgs boson. With the full Run3 data, evidence for this decay might be reached, or at least important enhancements of its branching ratio due to non-Standard Model effects could be excluded. The thesis will also include work on the ATLAS detector performance and contributions to the construction of the upgraded tracking detector (ITk) of ATLAS. Regular missions to CERN will be performed by the student to attend analysis meetings and present the results of their work.