Search for heavy Majorana neutrinos in vector boson scattering with $\ddot{I}„$-lepton final states with the ATLAS detector

Abstract

A search for heavy Majorana neutrinos coupling to third-generation leptons in vector boson scattering at the LHC is presented. The search is performed in the final state with a same-sign $\ddot{I}„\ddot{I}„$, $e\ddot{I}„$ or $\hat{I}¼\ddot{I}„$ pair using data of proton--proton collisions at $\sqrt{s}$ = 13 TeV, recorded with the ATLAS detector and corresponding to an integrated luminosity of 140 ${\text{fb}}^{-1}$. No significant deviation from the Standard Model background is observed. Constraints on the squared mixing matrix element between the $\ddot{I}„$-lepton and the heavy Majorana neutrino ($|V_{\ddot{I}„N}{|}^2$) are derived for heavy Majorana neutrino masses between 92 GeV and 6.5 TeV. Additionally, two-dimensional constraints on ($|V_{eN}{|}^2,|V_{\ddot{I}„N}{|}^2$) and ($|V_{\hat{I}¼N}{|}^2,|V_{\ddot{I}„N}{|}^2$) are set. These results improve the limits on heavy Majorana neutrinos coupling to third-generation leptons for heavy Majorana neutrino masses above 1.0 TeV, and extend the exclusion limits to an unexplored mass range above 1.5 TeV.

32 pages in total, author list starting page 16, 4 figures, 1 table, submitted to PRL. All figures including auxiliary figures are available at: https://atlas.web.cern.ch/Atlas/GROUPS/PHYSICS/PAPERS/EXOT-2025-05/

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