Search for pairs of highly collimated groupings of photons at 13 TeV with the ATLAS detector

Results of a search for the pair production of highly collimated groupings of photons (photon jets) in the ATLAS detector at the LHC are reported, using data from proton-proton collisions collected in 2015 and 2016 at a centre-of-mass energy of 13 TeV. Photon-jets can arise from the decay of new, highly boosted particles that are identified in the electromagnetic calorimeter as a single, photon-like cluster by the trigger system.