Abstract
Most searches for top partners, T , are concerned with top partner pair production. However, as these bounds become increasingly stringent, the LHC energy will saturate and single top partner production will become more important. In this paper we study the novel signature of the top partner produced in association with the SM top, ppto Toverline{t}+toverline{T} , in a model where the Standard Model (SM) is extended by a vector-like SU(2)L singlet fermion top partner and a real, SM gauge singlet scalar, S. In this model, ppto Toverline{t}+toverline{T} production is possible through loops mediated by the scalar singlet. We find that, with reasonable coupling strengths, the production rate of this channel can dominate top partner pair production at top partner masses of mT ≳ 1.5 TeV. In addition, this model allows for the exotic decay modes T → tg, T → tγ, and T → tS. In much of the parameter space the loop induced decay T → tg dominates and the top partner is quite long lived. New search strategies are necessary to cover these decay modes. We project the the sensitivity of the high luminosity LHC to ppto Toverline{t}+toverline{T} via a realistic collider study. We find with 3 ab−1, the LHC is sensitive to this process for masses mT ≲ 2 TeV. In addition, we provide appendices detailing the renormalization of this model.
Highlights
Background generationThe Standard Model (SM) √backgrounds are generated by MadGraph5 aMC@NLO at leading order accuracy in QCD at S = 14 TeV with the NNPDF2.3QED parton distribution function [91]
In this paper we study the novel signature of the top partner produced in association with the SM top, pp → tT production (T t) + tT, in a model where the Standard Model (SM) is extended by a vector-like SU(2)L singlet fermion top partner and a real, SM gauge singlet scalar, S
We focus on the region of parameter space for which the scalar can be produced at the LHC with reasonable rates, i.e. mS ∼ 100s GeV and mT > mS
Summary
We consider a model consisting of a vector-like SU(2)L singlet top partner, T2, and a real SM gauge singlet scalar S. After EWSB, it is possible for the scalar S and Higgs boson h to mix. Since the focus of this paper is the production and decay of the top partner, for simplicity we set the scalar mixing angle to zero. H and S are mass eigenstates with masses mh = 125 GeV [80,81,82] and mS, respectively; such that h is the observed Higgs boson [83, 84] There is another possible simplification of the Lagrangian. The Higgs Yukawa coupling, yt, λt, and the vector like mass M2 can be expressed in terms of the mixing angle θL and masses mt, mT : M22 = m2T cos θL + m2t sin θL yt.
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