Search for vectorlikeBquarks in events with one isolated lepton, missing transverse momentum, and jets ats=8  TeVwith the AT

Abstract

A search has been performed for pair production of heavy vectorlike down-type (B) quarks. The analysis explores the lepton-plus-jets final state, characterized by events with one isolated charged lepton (electron or muon), significant missing transverse momentum, and multiple jets. One or more jets are required to be tagged as arising from b quarks, and at least one pair of jets must be tagged as arising from the hadronic decay of an electroweak boson. The analysis uses the full data sample of pp collisions recorded in 2012 by the ATLAS detector at the LHC, operating at a center-of-mass energy of 8 TeV, corresponding to an integrated luminosity of 20.3 fb −1 . No significant excess of events is observed above the expected background. Limits are set on vectorlike B production, as a function of the B branching ratios, assuming the allowable decay modes are B → Wt=Zb=Hb. In the chiral limit with a branching ratio of 100% for the decay B → Wt, the observed (expected) 95% C.L. lower limit on the vectorlike B mass is 810 GeV (760 GeV). In the case where the vectorlike B quark has branching ratio values corresponding to those of an SUð2Þ singlet state, the observed (expected) 95% C.L. lower limit on the vectorlike B mass is 640 GeV (505 GeV). The same analysis, when used to investigate pair production of a colored, charge 5=3 exotic fermion T 5=3 , with subsequent decay T 5=3 → Wt, sets an observed (expected) 95% C.L. lower limit on the T 5=3 mass of 840 GeV (780 GeV).

Bounding wide composite vector resonances at the LHC

“…In particular, an interesting decay channel is that of the neutral ρ into a pair of X 5/3 top partners with exotic electric charge 5/3. This channel gives rise to a distinctive same sign dilepton (SS2 ) signature which is currently exploited both by the ATLAS and CMS collaborations to bound the X 5/3 mass through QCD-driven pair production [20,21]. We point out in this paper that a simple reinterpretation of these analyses offers an interesting possibility to probe the otherwise elusive EW spin one resonances in a regime where they dominantly decay into top partners.…”

“…This final state configuration is subject to a significantly smaller SM backgrounds with respect to other top partner search channels, and it can thus be used as a powerful experimental probe. It is in fact currently exploited by both ATLAS and CMS collaborations to bound X 5/3 states pair produced through QCD interactions, setting a limit of m X 5/3 800 GeV at 95% confidence level (CL) [20,21].…”

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.…”

Future collider signatures of the possible 750 GeV state

“…This is particularly true in the case of vector-like partners of the top and bottom quarks. Indeed, depending on the decay branching fractions, one has for instance the bounds m T > 950 GeV for a branching ratio BR(T → ht) = 1 and m B > 813 GeV for if BR(B → W t) = 1 [155][156][157][158]. (Similar limits can be set on quarks with exotic charges that we do not discuss here.)…”