New Particles and Interactions

Abstract

We analyze the manifestations of new matter particles predicted by models of new physics beyond the Standard Model, at present and future high-energy colliders. We consider both the production of these new particles and some of their indirect signatures at pp and eP colliders as well as TeV e + e − colliders with their e + e − , eγ, γγ and e − e − modes. The report is arranged into four main sections plus an overview. These sections will deal separately with exotic and excited fermions, difermions, and new interactions.To appear as a chapter in Electroweak Symmetry Breaking and Beyond the Standard Model, edited by T. Barklow, S. Dawson, H.E. Haber and S. Siegrist, World Scientific.1 Work supported by the Department of Energy, contract DE-AC03-76SF00515. OverviewMany theories beyond the Standard Model (SM) of the electroweak and strong interactions, predict the existence of new matter particles. These new particles can be cast into three categories: exotic fermions, excited fermions and difermions. A fourth category will consist in supersymmetric particles but these will be discussed in a different report. a) Exotic Fermions. New fermions are predicted by many gauge extensions of the SM and often, they have the usual lepton and baryon quantum number but non-canonical SU(2) L ×U(1) Y quantum numbers, e.g. the left-handed (LH) components are in weak isosinglets and/or the right-handed (RH) components in weak isodoublets. Examples of these exotic fermions are the following [1].i) Sequential fermions: they exist in the simplest extension of the SM where one simply has to add to the known fermionic spectrum with its three-fold replica a fourth family with the same quantum numbers. The existence of a fourth generation is still allowed by experimental data, if the associated neutrino is heavy enough [2]. This heavy neutrino should have a RH component in order that one can generate its mass, using the Higgs mechanism, in a gauge invariant way.ii) Vector fermions: these occur for instance in the E 6 group [3], which is suggested as a low energy limit of superstring theories. In E 6 , each fermion generation lies in the representation of dimension 27, and in addition to the fifteen SM chiral fields, twelve new fields are needed to complete this representation. Among these, there will be two weak isodoublets of heavy leptons, a RH and a LH one.iii) Mirror fermions: they have chiral properties which are opposite to those of ordinary fermions, i.e. the RH components are in weak isodoublets and the LH ones are in weak isosinglets; there is also a LH heavy neutrino [4]. These fermions appear in many extensions of the SM and provide a possible way to restore leftright symmetry at the scale of the electroweak symmetry breaking; they naturally occur in lattice gauge theories [5].iv) Singlet fermions: these are the most discussed fermions in the literature, a prominent example being the SO(10) neutrino [6,7,8]. Indeed, in this unifying group, which is one of the simplest and most economic extensions of the SM, the smallest ...

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“…This will reduce the singly-resonant and non-resonant backgrounds, and is accomplished by selecting events which satisfy either Imposing the cuts listed in Eqs. (23)(24)(25)(26)(27)(28), and before taking into account particle identification efficiencies, we obtain a cross section of about 5 fb (82 fb) at the Tevatron (LHC). The total integrated luminosity one hopes to achieve at the Tevatron in Run II is between 4 and 8 fb −1 .…”

“…The cuts imposed are listed in Eqs. (23)(24)(25)(26)(27)(28). No particle ID efficiencies are included here.…”

“…The ttγ and ttZ couplings can also be tested in e + e − → tt [16][17][18][19][20][21][22], and in ttV (V = γ, Z) production at hadron colliders [23,24]. Finally, the process γγ → tt is also sensitive to ttγ couplings [25,26].…”

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“…Once the new particles are discovered, their standard-model quantum numbers can be worked out from their production cross sections and asymmetries, and their couplings to lighter states from their branching ratios. A recent survey of exotic particles can be found in [235]. Specific examples that have been discussed in detail include heavy neutral leptons [236], excited leptons and quarks [237], and leptoquarks [238].…”