Searches for exclusive Higgs boson decays into D^⁎γ and Z boson decays into D*γ and K⁰_Sγ in pp collisions at √s = 13 TeV with the ATLAS detector

Searches for exclusive decays of the Higgs boson into D^⁎γ
and of the Z boson into D⁰γ and K⁰_sγ 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 D⁰γ channels, the observed (expected) 95% confidence-level upper limits on the respective branching fractions are B(H → D^⁎γ) < 1.0(1.2) x 10^-3, B(Z →D⁰γ) < 4.0(3.4) x 10^-6 , while the corresponding results in the K⁰_sγ channel are B(Z→K⁰_sγ) , 3.1 (3.0) x 10^-6.