Bridging grant application for ATLAS-Canada; Prompt and Long-Lived Particles - Searching for new physics at the Energy Frontier

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The proposed research program will act as a bridge to my participation in the ATLAS experiment at the Large Hadron Collider (LHC) at CERN. As a new faculty member in Canada at Simon Fraser University, this initial NSERC Discovery Grant will fund the initiation of my new research program, which will then continue with funding made available by a renewal of the NSERC ATLAS-Canada project grant during the 2021 competition. This application describes the program that I will initiate during this year (request for one year) and that I expect to carry out within the next five years. These funds will allow me to establish an outstanding research program, address imminent challenges ahead of the next LHC data taking period (starting 2021), and enhance Canada's role in one of the world's most highly regarded scientific endeavors. The Standard Model is like Newtonian physics - a success story: it describes all visible matter in the Universe and all forces (with the exception of gravity), and it describes how elementary particles acquire a mass (Higgs mechanism). All predictions have been verified by experiment with excellent precision for more than 50 years. The last piece to this puzzle was added in 2012: the Higgs boson discovery by the ATLAS and CMS experiments. Now we test the limits of this SM in order to find an inconsistency and ascertain clues about physics Beyond the Standard Model (BSM). One promising way to reveal such clues is to push to high energies, where we expect a new theory to reveal itself. The LHC is the most powerful particle accelerator ever built and provides a unique opportunity to explore this high-energy frontier. My primary objective here will be to use the ATLAS detector to search for signs of long-lived new particle (LLP) signatures in order to shed light on the universe's biggest remaining mysteries: why matter prevailed over antimatter in the early universe and what dark matter is. Searching for these particles is highly challenging, as they tend not to interact with other matter, making them elusive to detection. The overwhelming majority of searches for new physics at the LHC have been performed under the assumption that the new particles decay promptly, i.e., very close to the proton-proton interaction point. However, particles in the SM have lifetimes () spanning an enormous range of magnitude, from the Z boson (10-25s) through to the proton (>1034y) and electron (stable). Similarly, BSM models typically predict new particles with a variety of lifetimes. BSM LLPs may have macroscopic, detectable displacements between their production and decay points within the detector. Their unusual signatures offer excellent prospects for the discovery of new physics at particle colliders during the next data-taking period. At the same time, standard reconstruction algorithms may reject events or objects containing LLPs precisely because of their unusual nature, and dedicated searches are needed to uncover LLP signals.