NA62 sensitivity to heavy neutral leptons in the low scale seesaw model

TL;DR

This paper analyzes how neutrino oscillation data constrains heavy neutral lepton couplings in the low scale seesaw model and estimates NA62 experiment sensitivity variations based on these constraints.

Contribution

It provides a detailed study of neutrino oscillation constraints on heavy neutrino mixing and evaluates NA62 sensitivity in different benchmark scenarios.

Findings

Neutrino oscillation data significantly constrains heavy neutrino flavor mixing patterns.

NA62 sensitivity can vary by nearly two orders of magnitude depending on model parameters.

Sensitivity is only weakly dependent on flavor mixing within preferred parameter ranges.

Abstract

The sensitivity of beam dump experiments to heavy neutral leptons depends on the relative strength of their couplings to individual lepton flavours in the Standard Model. We study the impact of present neutrino oscillation data on these couplings in the minimal type I seesaw model and find that it significantly constrains the allowed heavy neutrino flavour mixing patterns. We estimate the effect that the DUNE experiment will have on these predictions. We then discuss implication that this has for the sensitivity of the NA62 experiment when operated in the beam dump mode and provide sensitivity estimates for different benchmark scenarios. We find that the sensitivity can vary by almost two orders of magnitude for general choices of the model parameters, but depends only weakly on the flavour mixing pattern within the parameter range that is preferred by neutrino oscillation data.