Search for New Physics at the Large Hadron Collider in a Topology with a Single Tau Lepton, Missing Transverse Momentum, and a Boosted Jet

Abstract

One of the most notable downfalls of the standard model (SM) and some of its theoretical extensions is the inability to provide a Dark Matter (DM) particle candidate with characteristics such that DM + DM ↔ SM + SM interactions in the early universe produce the correct DM relic density measured in astronomy probes. We conduct a search for new physics at the Large Hadron Collider (LHC) in the context of two models featuring coannihilation mechanisms that resolve this observed discrepancy. Supersymmetry (SUSY) provides a DM candidate in the form of the lowest supersymmetric particle (LSP), the lightest neutralino, which can theoretically be produced at the LHC. We also consider a novel model that predicts a new scalar or vector boson, referred to as a leptoquark (LQ) in the literature. The LQ enables quark-lepton interactions at high energy scales, thus carries both lepton and baryon number. We search for LQ production at the LHC in the context of a LQ-portal DM simplified model. For the considered coannihilation mechanisms to yield predictions that align with astronomical measurements, the mass difference between coannihilating partners must be small, resulting in low-momentum decay products. To provide a momentum boost to our system and enhance sensitivity, we require a high-momentum jet in our event selections, along with missing momentum due to the presence of our DM candidate. Due to experimental evidence suggesting enhanced couplings to third-generation leptons and naturalness arguments in SUSY, we look to the SM tau as our signature decay product in our event selections.