Top Partner Production Research Articles

Fully hadronic decays of a singly produced vectorlike top partner at the LHC

Single production of vectorlike top partners is becoming a major focus of new searches, as the increasing mass limits on vectorlike quarks obtained by the ATLAS and CMS collaborations are such that single production is becoming competitive with respect to pair production. Typically searches focus on decays containing leptons in the final state in order to have less background from the Standard Model processes. However the current centre of mass energies available in the latest LHC runs limit the searches to low masses. Fully hadronic final states may be an alternative option for discovery, as they allow a larger number of signal events if backgrounds can be kept under control. We study the fully hadronic decay of a singly produced vectorlike top partner and we show a strategy to extract the signal over the background, considering as a benchmark the $20\text{ }\text{ }{\mathrm{fb}}^{\ensuremath{-}1}$ of data collected at 8 TeV with the run I of the LHC.

Search for pair production of third-generation scalar leptoquarks and top squarks in proton–proton collisions at [formula omitted

A search for pair production of third-generation scalar leptoquarks and supersymmetric top quark partners, top squarks, in final states involving tau leptons and bottom quarks is presented. The search uses events from a data sample of proton–proton collisions corresponding to an integrated luminosity of 19.7 fb−1, collected with the CMS detector at the LHC with s=8 TeV. The number of observed events is found to be in agreement with the expected standard model background. Third-generation scalar leptoquarks with masses below 740 GeV are excluded at 95% confidence level, assuming a 100% branching fraction for the leptoquark decay to a tau lepton and a bottom quark. In addition, this mass limit applies directly to top squarks decaying via an R-parity violating coupling λ333′. The search also considers a similar signature from top squarks undergoing a chargino-mediated decay involving the R-parity violating coupling λ3jk′. Each top squark decays to a tau lepton, a bottom quark, and two light quarks. Top squarks in this model with masses below 580 GeV are excluded at 95% confidence level. The constraint on the leptoquark mass is the most stringent to date, and this is the first search for top squarks decaying via λ3jk′.

Reconstructing singly produced top partners in decays toWb

Fermionic top partners are a feature of many models of physics beyond the Standard Model. We propose a search strategy for single production of top partners focussing specifically on the dominant decay to $Wb$. The enormous background can be reduced by requiring a forward jet and exploiting jet substructure to suppress top-pair production. This simple strategy is shown to produce a sensitive search for single top-partner production, in the context of composite Higgs models, that has competitive mass reach with existing experimental searches for top-partner-pair production at the 8TeV LHC.

Tracking down the top quark forward-backward asymmetry with monotops

We revisit the possibility that the top quark forward-backward asymmetry arises from the on-shell production and decay of scalar top partners to $t\overline{t}+{\mathrm{E\ensuremath{\llap{\not\;}}}}_{T}$. Although the asymmetry is produced by $t$-channel exchange of a light mediator, the model remains unconstrained by low energy atomic parity violation tests. An interesting connection to the active neutrino sector through a type-I seesaw operator helps to evade stringent monojet constraints and opens up a richer collider phenomenology. After performing a global fit to top data from both the Tevatron and the LHC, we obtain a viable region of parameter space consistent with all phenomenological and collider constraints. We also discuss the discovery potential of a predicted monotop signal and related lepton charge asymmetry at the LHC.

Single vector-like top partner production in the left-right twin Higgs model at TeV energy eγ colliders

The left-right twin Higgs model contains a new vector-like heavy top quark, which mixes with the SM-like top quark. In this work, we studied the single vector-like top partner production via process e−γ → νeT̄b at the International Linear Collider. We calculated the production cross section at tree level and displayed the relevant differential distributions. The result shows that there will be 125 events produced each year with √s=2 TeV and the integrated luminosity ℒint ≈ 500 fb−1, and the b-quark tagging and the relevant missing energy cut will be helpful to detect this new effect.

Search for exotic same-sign dilepton signatures (b' quark, T5/3 and four top quarks production) in 4.7 fb−1 of pp collisions at = 7 TeV with the ATLAS detector

We present a search for pair production of down-type heavy quarks (b'b̄'), single and pair production of heavy top quark partners (T5/3qq̄' and T5/3T̄5/3, respectively), and production of events containing four top quarks (ttt̄t) in pp collisions at = 7 TeV recorded with the ATLAS detector at the LHC. For an integrated luminosity of 4.7 fb−1, the corresponding lower limit on both the b' and T5/3 mass is 0.67 TeV at 95% confidence level, when produced in pairs. When including the single production mechanism, limits on T5/3 production are 0.68 TeV and 0.70 TeV for a coupling constant of the tWT5/3 vertex equal to 1 and 3, respectively. The upper limit on the four top quarks production cross section is 61 fb at 95% confidence level.

Phenomenology of top partners at the ILC

The assumption of a new symmetry provides a nice explanation of the existence of dark matter and an elegant way to avoid the electroweak constraints. This symmetry often requires the pair production of new particles at colliders and it guarantees that cascade decays down to the lightest particle give rise to missing energy plus jets and leptons. For a long time, supersymmetry with the conserved R-parity was the only candidate for such signals. However, any new physics with this type of new symmetry may show up with similar signals and the discrimination between different models at the LHC is quite challenging. In this paper, we address the problem of discrimination between different models, more concretely, in the little Higgs theory with T-parity (LHT) and the supersymmetric theory with R-parity. We concentrate on the pair production of heavy top partners, e.g., T-odd quarks in LHT and the scalar top quarks in the MSSM at linear colliders (LC).