Abstract

A direct search for the Standard Model Higgs boson decays to a pair of charm quarks is presented, probing the Higgs boson Yukawa couplings to the second generation of fermions. This analysis makes use of the full LHC Run 2 dataset collected with the ATLAS detector, corresponding to an integrated luminosity of 139 ifb of proton collisions at a centre-of-mass energy of 13 TeV. An extrapolation of this search to the HL-LHC conditions - a centre-of-mass energy of 14 TeV, an integrated luminosity of 3000 ifb - is also presented. The production of the Higgs boson in association with a W or Z boson is targeted, where only leptonic decays of the W or Z boson are considered. Both charm and bottom jet tagging algorithms are used to identify the signature of the Higgs boson decay to charm quarks, while reducing contamination from Higgs boson decays to bottom quarks. The full Run 2 search improves the constraint on the cross-section times branching fraction for a Higgs boson with a mass of 125 GeV previously presented by ATLAS, using an integrated luminosity of 36 ifb of proton-proton collisions at the same centre-of-mass energy. A direct limit on the charm Yukawa coupling modifier from Higgs boson to charm quark decays is also set. The HL-LHC extrapolation of this search has the potential to further improve the constraints.