Search for Dark Matter produced in association with a Standard Model Higgs Boson decaying to b-quarks with the ATLAS detector

Abstract

The Standard Model (SM) of particle physics has been immensely successful in explaining elementary particles and how they interact with each other. However, SM alone is insufficient to answer many open questions in modern physics, such as the presence of dark matter (DM) and dark energy (DE) in our universe. Ordinary matter, observed so far by various experiments, accounts for only about 5% of the energy density of the universe, while a large fraction is in the form of DM (∼27%) and DE (∼68%). While the nature of DM is still unknown, one of the leading hypotheses suggests that it consists of Weakly Interacting Massive Particles (WIMP). All evidence point to the interaction between DM and SM to be very weak. DM searches are being pursued in collider experiments alongside direct and indirect detection experiments. Since the DM particles would interact very weakly with the detector they would escape undetected. This will induce a momentum imbalance in the transverse plane of the plane where interactions are taking place, also known as the missing transverse energy (ETmiss). Since at the LHC the ETmiss can only be evaluated in the presence of visible SM particles, the DM searches are performed in association with SM particles that can be detected at the LHC. In this document, a search for dark matter candidates produced in association with a Standard Model Higgs boson decaying to two b-jets is presented. The search uses a dataset of pp collisions at √s = 13 TeV corresponding to an integrated luminosity of 139 fb−1, recorded by the ATLAS detector. The results are interpreted in the context of the Two-Higgs Doublet Model (2HDM) with an additional vector or pseudoscalar mediator. The 2HDM is connected to the so-called Higgs portal models, in which DM particles interact with the SM particles only through their couplings with the Higgs sector. The analysis did not discover any DM particles and constraints are put on the model parameters. Some parts of the benchmark DM model phase-space are excluded and improvements are observed compared to previous results. © Copyright owned by the author(s) under the terms of the Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International License (CC BY-NC-ND 4.0)