Abstract

In the Standard Model (SM) the mass generation of fermions is implemented through Yukawa couplings to the Higgs boson. For quarks, direct evidence exists only for the third-generation couplings, and direct searches for inclusive decays of the Higgs boson to lighter generations are challenging due to large QCD backgrounds at the LHC. With their distinct experimental signature, exclusive radiative decays of the Higgs boson to a meson and a photon, complemented by searches for analogous decays of the Z boson, offer an alternative probe of quark Yukawa couplings. Moreover, these decays provide an opportunity to investigate physics beyond-the-SM, as many such theories predict branching fractions significantly modified from the SM expectation. This seminar will cover the results of the latest searches from the ATLAS experiment, including for the Higgs and Z boson decays to a quarkonium state and a photon, an omega meson and a photon, and the flavour-changing Higgs boson decay to a K* meson and a photon.