Abstract
A search is presented in proton-proton collisions at √s = 7 TeV for fermionic triplet states expected in type III seesaw models. The search is performed using final states with three isolated charged leptons and an imbalance in transverse momentum. The data, collected with the CMS detector at the LHC, correspond to an integrated luminosity of 4.9 fb -1 . No excess of events is observed above the background predicted by the standard model, and the results are interpreted in terms of limits on production cross sections and masses of the heavy partners of the neutrinos in type III seesaw models. Depending on the considered scenarios, lower limits are obtained on the mass of the heavy partner of the neutrino that range from 180 to 210 GeV. These are the first limits on the production of type III seesaw fermionic triplet states reported by an experiment at the LHC.
Highlights
Ideas beyond the standard model have been proposed to accommodate the finite values of neutrino masses inferred from neutrino oscillations
This paper reports on a search for fermionic triplet states (Σ) expected in type III seesaw models, in final states with three charged leptons and an imbalance in transverse momentum
Three types of SM processes can produce a three-lepton final state: (i) events containing three or more prompt leptons from production and leptonic decays of two or three electroweak (EW) bosons; (ii) V + γ and V + γ∗ events, where V represents any EW boson, with the accompanying photons converting to l+l−; and (iii) events with one or two prompt leptons and additional non-prompt leptons that arise from leptonic decays of hadrons within jets, called “misidentified jets”. (i) The irreducible background is dominated by SM W+Z production, and includes ZZ and three-boson events
Summary
Ideas beyond the standard model have been proposed to accommodate the finite values of neutrino masses inferred from neutrino oscillations. An interesting possibility is provided by the seesaw mechanism, in which a small Majorana mass can be generated for each of the known neutrinos by introducing massive states with Yukawa couplings to leptons and to the Higgs field. Seesaw models called type I, type II, and type III introduce heavy states of mass M, that involve, respectively, weak-isospin singlets, scalar triplets, and fermion triplets Seesaw models called type I, type II, and type III introduce heavy states of mass M, that involve, respectively, weak-isospin singlets, scalar triplets, and fermion triplets (Ref. [1])
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