Article

# Next-to-Leading Order Cross Sections for New Heavy Fermion Production at Hadron Colliders

(Impact Factor: 4.64). 09/2009; 81(3). DOI: 10.1103/PhysRevD.81.035006
Source: arXiv

ABSTRACT

We evaluate the cross sections for new heavy fermion production at three
perturbative quantum chromodynamics. We treat the cases of pair production of
heavy quarks via strong interactions, single heavy quark production via
electroweak interactions, and the production of heavy leptons. Theoretical
uncertainties associated with the choice of the renormalization scale and the
parton distribution functions are specified. We derive a simple and useful
parameterization of our results which should facilitate phenomenological
studies of new physics models that predict new heavy quarks and/or leptons.

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Available from: Qing-Hong Cao,
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• "The analyses carried out by the ATLAS and CMS collaborations assume pair production of the heavy top quark. This production mode is dominated by QCD production, and the cross section is determinable in a model independent fashion from the work in [49], or using the HATHOR coding package [50]. In particular, we focus on the CMS results and similarly use the HATHOR package to calculate our production cross sections. "
##### Article: Vector-like quarks with a scalar triplet
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ABSTRACT: We study a model independent extension to the Standard Model with an addi- tional real scalar triplet, {\Sigma}, and a single vector-like quark, T . This class of models appear naturally in extensions of the Littlest Higgs model that incorporate dark matter without the need of T -parity. We assume that the triplet does not develop a vacuum expectation value and that all dimension five operators coupling the triplet to Standard Model fields and the vector-like quarks are parametrized by the scale {\Lambda} at which we expect new physics to arise. We introduce new non-renormalizable interactions between the new scalar sector and fermion sector that allow mixing between the Standard Model third generation up-type quark and the vector-like quark in a way that leads to the cancellation of the leading quadratic divergences to the one-loop corrections to the mass of the Higgs boson. Within this framework, new de- cay modes of the vector-like quark to the real scalar triplet and SM particles arise and bring forth an opportunity to probe this model with existing and future LHC data. We contrast constraints from direct colliders searches with low energy precision measurements and find that heavy vector-like top quarks with a mass as low as 650 GeV are consistent with current experimental constraints in models where new physics arises at scales below 2 TeV. Lastly, we discuss a model where new decay modes of the heavy vector-like top quarks are possible within an extension of the Littlest Higgs model.
Physics Letters B 09/2014; 716. DOI:10.1016/j.physletb.2015.02.071 · 6.13 Impact Factor
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• "Previous direct searches restrict the masses of quarks in the fourth generation, M t and M b , to be greater than 404 and 372 GeV/c 2 , respectively [7] [8], and the measurement of the Z lineshape at the Large Electron-Positron collider excludes a fourth generation of light neutrinos [9] [10] [11] [12]. At the Large Hadron Collider (LHC), the quantum chromodynamics (QCD) production cross section of t t is expected to be two orders of magnitude larger than that at the Tevatron for M t = 500 GeV/c 2 [13]. This increase provides an opportunity to explore the possibility of new physics with an extended generation of fermions at higher masses. "
##### Article: Search for heavy, top-like quark pair production in the dilepton final state in $pp$ collisions at $sqrts = 7$ TeV
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ABSTRACT: The results of a search for pair production of a heavy, top-like quark, t', in the decay mode (t' anti-t') to (b anti-W anti-b W) to (b anti-lepton neutrino anti-b lepton anti-neutrino) are presented. The search is performed with a data sample corresponding to an integrated luminosity of 5.0 inverse femtobarns in pp collisions at a center-of-mass energy of 7 TeV, collected by the CMS experiment at the LHC. The observed number of events agrees with the expectation from standard model processes, and no evidence of t' anti-t' production is found. Upper limits on the production cross section as a function of t' mass are presented, and t' masses below 557 GeV/c^2 are excluded at the 95% confidence level.
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##### Article: Dynamical electroweak symmetry breaking with superheavy quarks and 2+1 composite Higgs model
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ABSTRACT: Recently, a new class of models describing the quark mass hierarchy has been introduced. In this class, while the t quark plays a minor role in electroweak symmetry breaking (EWSB), it is crucial in providing the quark mass hierarchy. In this paper, we analyze the dynamics of a particular model in this class, in which the b' and t' quarks of the fourth family are mostly responsible for dynamical EWSB. The low energy effective theory in this model is derived. It has a clear signature, a 2 + 1 structure of composite Higgs doublets: two nearly degenerate \Phi_{b'} and \Phi_{t'}, and a heavier top-Higgs resonance \Phi_t \sim \bar{t}_{R}(t,b)_L. The properties of these composites are described in detail, and it is shown that the model satisfies the electroweak precision data constraints. The signatures of these composites at the Large Hadron Collider are briefly discussed. Comment: 17 pages, 3 figures; v.2: references and clarifications added: PRD version
Physical review D: Particles and fields 12/2009; 81(5). DOI:10.1103/PhysRevD.81.055014 · 4.86 Impact Factor