Search for pair-produced vectorlikeBquarks in proton-proton collisions ats=8  TeV

Abstract

A search for the production of a heavy B quark, having electric charge −1=3 and vector couplings to W, Z, and H bosons, is carried out using proton-proton collision data recorded at the CERN LHC by the CMS experiment, corresponding to an integrated luminosity of 19.7 fb −1 . The B quark is assumed to be pair produced and to decay in one of three ways: to tW, bZ, or bH. The search is carried out in final states with one, two, and more than two charged leptons, as well as in fully hadronic final states. Each of the channels in the exclusive final-state topologies is designed to be sensitive to specific combinations of the B quarkantiquark pair decays. The observed event yields are found to be consistent with the standard model expectations in all the final states studied. A statistical combination of these results is performed, and upper limits are set on the cross section of the strongly produced B quark-antiquark pairs as a function of the B quark mass. Lower limits on the B quark mass between 740 and 900 GeV are set at a 95% confidence level, depending on the values of the branching fractions of the B quark to tW, bZ, and bH. Overall, these limits are the most stringent to date.

Tadpole-induced electroweak symmetry breaking and pNGB Higgs models

“…However, in 'maximally natural' models, the full global symmetry is likely restored not too far above m T (see section 2.2). As a result, searches for other states implied by the global symmetry, such as heavy charge-1/3 Bquarks [67,68] or exotic charge-5/3 quarks [67,69] (present in complete multiplets of custodial SO(4)) may also be relevant [70,71]. In particular, for Twin Higgs models, the lightest top partner responsible for regulating the quadratic divergences is uncolored, leading to weak constraints from the LHC.…”

Spontaneous CP violation and the strong CP problem in left-right symmetric theories

“…Current LHC constraints from Atlas and CMS on vectorlike quarks can be found in Ref. [58][59][60][61][62][63][64] and give an approximate lower bound…”

Composite Higgs models with a hidden sector

“…Pairs of the lightest top quark partner t t and peculiar quark p p can also be strongly produced with cross sections as high as ∼ 5 fb in the viable regions of parameter space. The strongest limits on vector-like quarks are set by the CMS search at √ s =13 TeV in the single lepton channel [33,34]. These limits are driven by kinematically optimized searches for tt + X and bb + X where X = W, Z, h is highly boosted, and are interpreted in the context of simplified models that assume BR(t Z t) + BR(t h t) + BR(t W b) = 1.…”

“…However the branching fractions of the lightest BSM states to the singlet η are generically small. The lightest colorcharged states in such models would thus be virtually indistinguishable from the top and bottom partners of simplified models [33,34] and their phenomenology will not be discussed further here. The phenomenological signatures of of the hidden-sector in this model are similar to those described in Section II C 3 and will also not be reiterated here.…”