Search for Higgs boson decays to two bottom and charm quarks at ATLAS

The Higgs boson, the mass mediator in the Standard Model (SM) of particle physics, was discovered at the Large Hadron Collider (LHC) in 2012. Since then, measuring the decay from the Higgs boson to fermions and validating the SM prediction has been one of the main physics goals of the LHC. The Higgs boson to bottom quark decay (H->bb) has been observed by the ATLAS collaboration during the LHC second data run (Run 2). Similarly, upper limits have been set on the probability of Higgs bosons decaying to charm quarks (H->cc) using ATLAS Run 2 data. In this talk, we present the latest ATLAS combined measurement of the Higgs boson decays to bottom and charm quarks (H->bb,cc). Novel machine learning techniques are used to improve signal purity. This final ATLAS Run 2 combined measurement sets the most stringent upper limit on H->cc to date. In addition, this combined measurement orthogonalizes the event selection between H->bb and H->cc and correlates their modeling uncertainties. With the cancellation of uncertainties, the measurement sets the most stringent ratio between the charm and bottom Yukawa coupling modifiers (k_c/k_b) as well.