Exploring the Dark Sector with the ATLAS Detector

The presence of a non-baryonic Dark Matter component in the Universe is inferred from the observation of its gravitational interaction. If Dark Matter interacts weakly with the Standard Model (SM) it could be produced at the LHC. The ATLAS experiment has developed a broad search program for DM candidates, including resonance searches for the mediator which would couple DM to the SM as well as searches with large missing transverse momentum produced in association with other particles (quarks, photons, Z and H bosons) called mono-X searches and searches where the Higgs boson provides a portal to Dark Matter, leading to invisible Higgs decays. In the latter case, ATLAS also explores dark sector models where the Higgs boson can decay into a photon and an invisible dark photon. Furthermore, new particles with macroscopic lifetimes arise naturally in many beyond-the-standard-model scenarios. Long-lived particles are predicted in e.g. hidden valley models that include long lived mediators that decay to SM particles that leave striking and challenging signatures in the detector and maybe key to understanding naturalness and dark matter, and other outstanding questions in particle physics. The results of recent dark sector searches on 13 TeV pp data, their interplay and interpretation will be presented.