Indirect search of Heavy Neutral Leptons using the DUNE Near Detector

TL;DR

This paper assesses how the DUNE Near Detector can indirectly search for heavy neutral leptons by detecting deficits in neutrino events, providing improved bounds on their properties for certain mass ranges.

Contribution

It introduces a method to constrain heavy neutral leptons using neutrino deficit measurements at DUNE, extending sensitivity to masses between 1 eV and 500 MeV.

Findings

Limits on HNL mixing angles are improved for masses below 10 MeV.

DUNE can set competitive bounds on HNLs in the 40 eV to 1 MeV range.

Constraints are stronger with lower normalization uncertainties.

Abstract

We evaluate the potential of the DUNE Near Detector (DUNEND) for establishing bounds for heavy neutral leptons (HNL). This is achieved by studying how the presence of HNLs affects the production rates of active neutrinos, therefore, creating a deficit in the neutrino charged current (CC) events at the LArTPC of the DUNEND. The estimated bounds on HNLs are calculated for masses between 1 eV and 500 MeV. We consider 10 years of operation (5 in neutrino and antineutrino mode) and obtain limits of $|U_{\mu4}|^2 < 9 \times 10^{-3} (4 \times10^{-2})$ and $|U_{e4}|^2 < 7\times10^{-3} (3 \times10^{-2})$ for masses below 10 MeV and a 5\%(20\%) overall normalization uncertainty in the neutrino charged current event rates prediction. These limits, within the region of masses below 2(10) MeV, are better than those that can be achieved by DUNE direct searches for the case of a 5\%(20\%) uncertainty. When a conservative 20\% uncertainty is present, our limits can only improve current constraints on $|U_{e4}|^2$ by up to a factor of 3 in a small region around 5 eV and set limits on $|U_{\mu4}|^2$ in a mass region free of constraints (40 eV - 1 MeV).