Probing electroweak pair production of heavy neutral leptons with displaced vertices at the LHC

TL;DR

This paper investigates the potential of displaced vertex searches at the LHC to detect heavy neutral leptons produced in pairs, providing constraints and discovery prospects within a supersymmetric framework and beyond.

Contribution

It offers the first detailed analysis of displaced vertex sensitivity to heavy neutral leptons in a supersymmetric context, including constraints from Run 2 data and projections for future LHC runs.

Findings

Constraints on sterile neutrino masses between 20 and 230 GeV.

Active-sterile mixing angles down to 4×10⁻¹⁴ can be excluded.

Discovery potential for masses up to 295 GeV at HL-LHC.

Abstract

We study the sensitivity of displaced vertex searches at the LHC to heavy neutral leptons (also known as sterile neutrinos) that are produced in pairs with an electroweak-size cross section. We work within the context of a supersymmetric model in which the sterile neutrino is produced along with Standard Model particles in higgsino decays. By making use of model-independent reconstruction efficiencies provided by the ATLAS collaboration in their search for displaced vertices with multiple jets, we obtain constraints on this model from $139$ fb$^{-1}$ of data collected by ATLAS during the LHC Run~2, and assess the discovery reach of Run~3 and of the high-luminosity LHC (HL-LHC). Depending on the higgsino mass parameter, sterile neutrino masses between $20~\mathrm{GeV}$ and $230~\mathrm{GeV}$ and active-sterile neutrino mixings in the range $4 \times 10^{-14} \lesssim V^2_N \lesssim 3 \times 10^{-10}$ can be excluded. At the HL-LHC, discovery-level significances could be reached for sterile neutrinos masses up to $295~\mathrm{GeV}$ and values of $V^2_N$ down to $3 \times 10^{-14}$. Finally, moving away from the supersymmetric scenario, we study to which extent these results can be generalized to a broader class of models in which the sterile neutrinos are produced in the decays of heavier particles that are themselves pair-produced with an electroweak-size cross section.