Search for type-III Seesaw heavy leptons in $pp$ collisions at $\sqrt{s}=8$ TeV with the ATLAS Detector

Abstract

A search for the pair-production of heavy leptons ($N^0,L^{\pm }$) predicted by the type-III seesaw theory formulated to explain the origin of small neutrino masses is presented. The decay channels $N^0\to W^{\pm }{l}^{\mp }$ ($\ell =e,\mu ,\tau$) and $L^{\pm }\to W^{\pm }\nu$ ($\nu ={\nu }_e,{\nu }_{\mu },{\nu }_{\tau }$) are considered. The analysis is performed using the final state that contains two leptons (electrons or muons), two jets from a hadronically decaying $W$ boson, and large missing transverse momentum. The data used in the measurement correspond to an integrated luminosity of $20.3f{b}^{-1}$ of $pp$ collisions at $\sqrt{s}=8$ TeV collected by the ATLAS detector at the LHC. No evidence of heavy lepton pair-production is observed. Heavy leptons with masses below 325--540 GeV are excluded at the 95% confidence level, depending on the theoretical scenario considered.

11 pages plus author list + cover pages (22 pages total), 4 figures, 1 table, submitted to PRD, All figures including auxiliary figures are available at https://atlas.web.cern.ch/Atlas/GROUPS/PHYSICS/PAPERS/EXOT-2014-07/

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