Model-independent framework for searches of top partners

Abstract

We propose a model-independent and general framework to study the LHC phenomenology of top partners, i.e. Vector-Like quarks including particles with different electro-magnetic charge. We consider Vector-Like quarks embedded in general representations of the weak SU (2)L, coupling to all Standard Model quarks via Yukawa mixing focusing on the case of a single multiplet. We show that, with very minimal and quite general assumptions, top partners may be studied in terms of few parameters in an effective Lagrangian description with a clear and simple connection with experimental observables. We also demonstrate that the parametrisation can be applied as well to cases with many Vector-like multiplets, thus covering most realistic models of New Physics. We perform a numerical study to understand the conclusions which can be drawn within such a description and the expected potential for discovery or exclusion at the LHC. Our main results are a clear connection between branching ratios and single production channels, and the identification of novel interesting channels to be studied at the LHC.

Discovery potential for T ′ → tZ in the trilepton channel at the LHC

“…Although vector-like quarks are usually assumed to only mix with the third generation following hierarchy or naturalness arguments [14][15][16][17][18], the top partners can mix in a sizable way with lighter quarks while remaining compatible with the current experimental constraints [19,20]. This possibility has been recently pursued and must be considered with attention.…”

“…We will employ the dedicated model for the heavy singlet top partner as presented in ref. [20], comprising only 3 independent couplings.…”

“…A simple Lagrangian that parametrises the T ′ couplings to quarks and electroweak boson is (showing only the couplings relevant for our analysis) [20] where the subscripts L and R label the chiralities of the fermions. Only 3 parameters are sufficient to fully describe the interactions that are relevant for our investigation.…”

Light non-degenerate composite partners at the LHC

“…ref. [46,51] for a recent discussion of top partner signatures at the LHC.) Hence, we also point out the main phenomenological differences between top and up/charm partners in regard to production mechanisms and final states from their decay.…”

Single production of an exotic bottom partner at LHC

“…[22,23]. Bottom-like (B) and exotic quark of charge 5/3 (X) have been widely discussed also [24][25][26][27], see also [28,29]. These studies have motivated many searches that have putted stringent limits on the masses of the top partners.…”