MeV-scale sterile neutrino decays at the Fermilab Short-Baseline Neutrino program

TL;DR

This paper explores the potential of the Fermilab Short-Baseline Neutrino program to detect MeV-scale sterile neutrinos through their decay signatures, using simulations and considering detector capabilities.

Contribution

It introduces a comprehensive analysis of sterile neutrino decay channels at SBN, including neglected modes, and highlights the role of timing information for detection.

Findings

SBN can extend bounds on key sterile neutrino decay channels.

Liquid-Argon technology enables detection of previously neglected decay modes.

Improved timing resolution could directly observe sterile neutrino mass effects.

Abstract

Nearly-sterile neutrinos with masses in the MeV range and below would be produced in the beam of the Short-Baseline Neutrino (SBN) program at Fermilab. In this article, we study the potential for SBN to discover these particles through their subsequent decays in its detectors. We discuss the decays which will be visible at SBN in a minimal and non-minimal extension of the Standard Model, and perform simulations to compute the parameter space constraints which could be placed in the absence of a signal. We demonstrate that the SBN program can extend existing bounds on well constrained channels such as $N \rightarrow \nu l^+ l^-$ and $N \rightarrow l^\pm \pi^\mp$ while, thanks to the strong particle identification capabilities of liquid-Argon technology, also place bounds on often neglected channels such as $N \rightarrow \nu\gamma$ and $N \rightarrow \nu \pi^0$. Furthermore, we consider the phenomenological impact of improved event timing information at the three detectors. As well as considering its role in background reduction, we note that if the light-detection systems in SBND and ICARUS can achieve nanosecond timing resolution, the effect of finite sterile neutrino mass could be directly observable, providing a smoking-gun signature for this class of models. We stress throughout that the search for heavy nearly-sterile neutrinos is a complementary new physics analysis to the search for eV-scale oscillations, and would extend the BSM program of SBN while requiring no beam or detector modifications.