Search for Dark Matter Produced in Association with a Higgs Boson Decaying to a pair of bottom quarks with the ATLAS Detector

In this thesis, a search for dark matter production in association with a Higgs boson decaying to b-quarks is presented using pp collisions at a centre-of-mass energy of √s=13TeV. The results corresponds to a dataset with an integrated luminosity of 80fb−1, recorded with the ATLAS detector at the Large Hadron Collider. Selected collision events comprise large missing transverse momentum and either two b-tagged small radius jets or a single large radius jet containing two b-tagged subjets. The identification of these subjects is based on a jet algorithm where the radius parameter is shrinked as the transverse momentum increases. Also, with the help of a novel reconstruction technique, the object-based missing transverse momentum significance, it is shown that background coming from pure strong interactions can be successfully rejected. The results are interpreted in the context of a simplified model (Z′-2HDM) which describes the interaction of dark matter and standard model particles via new heavy mediator particles.