GeV-scale neutrinos: interactions with mesons and DUNE sensitivity

Abstract

The simplest extension of the SM to account for the observed neutrino masses and mixings is the addition of at least two singlet fermions (or right-handed neutrinos). If their masses lie at or below the GeV scale, such new fermions would be produced in meson decays. Similarly, provided they are sufficiently heavy, their decay channels may involve mesons in the final state. Although the couplings between mesons and heavy neutrinos have been computed previously, significant discrepancies can be found in the literature. The aim of this paper is to clarify such discrepancies and provide consistent expressions for all relevant effective operators involving mesons with masses up to 2 GeV. Moreover, the effective Lagrangians obtained for both the Dirac and Majorana scenarios are made publicly available as FeynRules models so that fully differential event distributions can be easily simulated. As an application of our setup, we numerically compute the expected sensitivity of the DUNE near detector to these heavy neutral leptons.

Hecate

“…been studied in[37] 4. The decay rates of HNLs into SM particles have been computed by many different authors[33,[38][39][40][41][42][43][44][45], they overall more or less agree with each other.…”

An allowed window for heavy neutral leptons below the kaon mass

“…We note that this is a conservative estimate and the actual sensitivity will be even higher as our analysis only included HNLs coming from D-mesons [78], while the HNLs originating from kaon decays will significantly increase the sensitivity [156]. [130]; the minimal mass will be pushed up to M N 0.39 GeV for both hierarchies. For SHiP, the minimal mass is M N ≈ 0.43(0.60) GeV for NH(IH).…”

“…The DUNE near detector will be very sensitive to HNLs [77,130,154]. In particular, it will be able to push the lower bound to M N = 0.39 GeV for both hierarchies and cover the open window at lower masses.…”

“…In particular, it will be able to push the lower bound to M N = 0.39 GeV for both hierarchies and cover the open window at lower masses. When estimating the sensitivity for DUNE we took U 2 e , U 2 µ bounds as reported in [130] and derived U 2 , U 2 τ bounds consistent with oscillation data. The SHiP experiment [155] at CERN will provide unprecedented sensitivity for heavy neutral leptons in the mass range of interest.…”

Light, long-lived B − L gauge and Higgs bosons at the DUNE near detector

“…The DUNE capability, specifically using its gaseous argon near detector (immediately downstream of the liquid argon near detector) to identify final-states of particles decaying in flight has been detailed in refs. [31,[44][45][46][47][48][49]. We will use the results of these works and consider that a background-free search for these final states is possible.…”