Testing Heavy Neutral Leptons in Cosmic Ray Beam Dump experiments

TL;DR

This paper explores the potential of cosmic ray beam dump experiments to detect Heavy Neutral Leptons (HNLs), proposing new observational setups and analyzing their sensitivity to untested parameter space.

Contribution

It introduces novel experimental configurations inspired by cosmic ray interactions and assesses their ability to probe unexplored HNL parameter regions.

Findings

Existing constraints exclude long-lived HNL explanations for certain cosmic phenomena.

A Cherenkov telescope at Mount Thor can test HNL masses below the kaon mass.

A geostationary satellite could explore HNL masses from 10 MeV to 2 GeV and neutrino mixing down to 10^{-11}.

Abstract

In this work, we discuss the possibility to test Heavy Neutral Leptons (HNLs) using $``$Cosmic Ray Beam Dump$"$ experiments. In analogy with terrestrial beam dump experiments, where a beam first hits a target and is then absorbed by a shield, we consider high-energy incident cosmic rays impinging on the Earth's atmosphere and then the Earth's surface. We focus here on HNL production from atmospherically produced kaon, pion and $D$-meson decays, and discuss the possible explanation of the appearing Cherenkov showers observed by the SHALON Cherenkov telescope and the ultra-high energy events detected by the neutrino experiment ANITA. We show that these observations can not be explained with a long-lived HNL, as the relevant parameter space is excluded by existing constraints. Then we propose two new experimental setups that are inspired by these experiments, namely a Cherenkov telescope pointing at the horizon and shielded by the mountain cliff at Mount Thor, and a geostationary satellite that observes part of the Sahara desert. We show that the Cherenkov telescope at Mount Thor can probe currently untested HNL parameter space for masses below the kaon mass. We also show that the geostationary satellite experiment can significantly increase the HNL parameter space coverage in the whole mass range from 10 MeV up to 2 GeV and test neutrino mixing $|U_{\alpha4}|^2$ down to $10^{-11}$ for masses around 300 MeV.