Searches for dark matter through new collider topologies

Abstract

This dissertation explores dark matter searches through new collider topologies using jets. A exploratory study, conducted in 2021, of dark photons in a search for dark matter is pre- sented. A dark photon may be detected through its kinetic mixing with the classical photon, which then couples weakly to electrically charged particles, allowing a non-gravitational window into the detection of dark matter. We will be considering the hypothetical Maver-ick top quark, in Ref [1], decaying to a Standard Model (SM) top quark and dark photon. The dark photon will decay exclusively to a lepton pair, for a dark photon mass up to 200 MeV the decay is completely to an electron and positron pair. We have focused on the hadronic decay of the top quark which gives a final state consisting of a heavy top quark jet. The search is for a large radius jet in the mass range of the top quark and a small radius jet close to the electron. We show that for a set of kinematic selections, almost all background can be eliminated, leaving enough signal events up to top partner mass of about 3.5 TeV for the search to be viable at the LHC Run 2. As well, a search is presented, conducted in 2022, for semi-visible jets arising from dark matter, using Run 2 data recorded with the ATLAS detector at the LHC with a center-of-mass energy of 13 TeV. For this search the hidden sector is hypothesized to couple to the SM via a heavy leptophobic Z′ mediator by a resonant production q ¯q → Z′ → χχ. Semi-visible jets present an unusual topology, where the visible states in the shower are SM hadrons and the strongly coupled hidden sector containing dark quarks resulting in dark hadrons. This gives a final state consist- ing of a jet aligned with missing transverse energy due a mixture of stable, invisible dark hadrons and visible hadrons from an unstable subset of dark hadrons that promptly decay to SM particles. The resonant production and decay of such a mediator will result in a dijet system of semi visible jets, a signature ignored by most dark matter searches. Finally a brief project investigating track reconstruction using quantum computing for LUXE is considered. The LUXE experiment is a new experiment in planning at DESY Hamburg which will investigate the non-perturbative QED regime. A study is presented to explore the potential of quantum computers to reconstruct positron trajectories from detector energy deposits. The reconstruction problem is formulated with a quadratic unconstrained binary optimisation and is a simple example of only 7 qubits. The results from quantum simulations are discussed and compared to results from a real IBM quantum device.