Search for Single Production of Vector-like Quarks (Top Partners) in the Multilepton Channel at the ATLAS Experiment at the LHC

This talk summarizes a search for a heavy, up-type vector-like quark (VLQ), or Top-partner, with charge +⅔. Top-partners are predicted in many well-motivated models of new physics beyond the Standard Model. The analysis uses 36.1/fb of pp collisions with a center of mass energy of 13 TeV at the LHC and recorded by the ATLAS detector to search for Top-partners resulting form the fusion of a W boson and a bottom quark and decaying into a Z boson and a top quark, resulting in a final state signature of two or three leptons. These leptons consist of a pair of opposite sign same flavor leptons from the decay of the Z boson as well as either a third lepton from the decay of the W boson, in association with a neutrino, or a hadronically decaying top quark. Since no evidence is found for a signal, upper limits have been placed on the production cross-section of VLQs. This talk will also present a generalized algebraic framework for interpreting the results of a generic search for the single production of VLQs in terms of the free parameters in the VLQ Lagrangian. It explains how this framework can be utilized to formulate a strategy for combination of multiple single VLQ searches.