Search for Dark Matter in final states with one photon and missing transverse momentum with the ATLAS experiment

A search for Dark Matter is conducted in final states containing a photon and missing transverse momentum in proton-proton collisions at a centreof- mass energy of 13 TeV. The data, collected during the period 2015–2018 by the ATLAS experiment at the CERN LHC, correspond to an integrated luminosity of 139 fb$^{-1}$. No deviations are observed relative to the predictions of the Standard Model and 95% confidence level (CL) upper limits, between 2.45 fb and 0.53 fb, are set on the visible cross section for contributions from physics Beyond the Standard Model, in different ranges of missing transverse momentum. The results are interpreted as exclusion limits in the models where weakly interacting Dark Matter candidates are pair-produced via an s-channel axial-vector or vector mediator. The search excludes mediators masses below 920–1470 GeV, and Dark Matter masses below 280–580 GeV at 95% CL, depending on the couplings. In addition, the results are expressed in terms of 95% CL limits on the parameters of a model with an axion-like particle produced in association with a photon.