Search strategies for vector-like quark partners at LHC run-II

Abstract

Abstract. We present results on several new search channels and strategies for heavy vector-like quark partners or vector resonances at the LHC run-II. Run-II has sensitivity to single-and pair-produced quark partners with masses beyond 1 TeV, and for even higher masses for vector resonances. Decays of such heavy particles yield highly boosted tops, Higgses, and weak gauge bosons. At high boost, the Standard Model background of hadronic final states can be substantially suppressed when applying jet-substructure techniques. We present several case studies where the identification of hadronically decaying tops, Higgses, and/or electroweak gauge bosons allow to make new search channels competitive at run-II. Motivation and OverviewNaturalness has for a long time been a guiding principle of theoretical particle physics. While the discovery of the last missing Standard Model SM particle -the Higgs -marks a great success of particle physics, it is difficult to understand why the Higgs mass is so much smaller than the Planck mass. Composite Higgs models provide a possible solution to this hierarchy problem [1,2]. The main idea behind composite Higgs models is to realize the Higgs multilplet as a light bound state of a theory which becomes strongly coupled below a scale of a few TeV. The large hierarchy between the TeV scale and the Planck scale is realized through dimensional transmutation. If the Higgs multiplet is realized as a pseudo-Nambu-Goldstone boson (pNGB) multiplet of a global symmetry of the underlying model, a small hierarchy between the Higgs mass m h , the electroweak scale v and the decay constant f of the pNGB can be realized at the price of a mild fine-tuning. From a low-energy perspective, the most minimal implementation of the composite Higgs paradigm is realized in models with S O(5) → S O(4) breaking [3]. Within such effective field theory descriptions, indirect bounds like deviations of Higgs couplings from the Standard Model (SM) prediction and electroweak precision tests yield constraints of f 500−1000 GeV, depending on the precise model, the top-partner masses, and the underlying UV dynamics. Flavour physics also yields important constraints, as obtaining the observed top mass requires an extended (top-)quark sector with additional sources for flavor changing neutral currents. Partial compositeness of the top can successfully address these flavor problems as recently discussed in [4].On the other hand, composite Higgs models can be tested directly by searching for composite resonances beyond the Higgs. Composite top-partners, scalar-or vector resonances are expected to