Searches for exclusive Higgs boson decays into D⁎γ and Z boson decays into D0γ and Ks0γ in pp collisions at s<mml:mo …

Searches for the exclusive decays of the Higgs boson into D^*γ and of the Z boson into D⁰γ and K⁰ₛγ can probe flavour-violating Higgs 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 D⁰γ 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→ D⁰γ)< 4.0 (3.4)× 10⁻⁶, while the corresponding results in the K⁰ₛγ channel are B(Z→ K⁰ₛγ)< 3.1 (3.0)× 10⁻⁶.