UC Irvine

Searches for exclusive decays of the Higgs boson into D ⁎ γ and of the Z boson into D 0 γ and K s 0 γ can probe flavour-violating Higgs boson and Z boson couplings to light quarks. Searches for these decays are performed with a pp collision data sample corresponding to an integrated luminosity of 136.3 fb−1 collected at s = 13 TeV between 2016–2018 with the ATLAS detector at the CERN Large Hadron Collider. In the D ⁎ γ and D 0 γ channels, the observed (expected) 95% confidence-level upper limits on the respective branching fractions are B ( H → D ⁎ γ ) < 1.0 ( 1.2 ) × 10 − 3 , B ( Z → D 0 γ ) < 4.0 ( 3.4 ) × 10 − 6 , while the corresponding results in the K s 0 γ channel are B ( Z → K s 0 γ ) < 3.1 ( 3.0 ) × 10 − 6 .