Neutrino-Portal Dark Matter Detection Prospects at a Future Muon Collider

TL;DR

This paper explores the potential of a future muon collider to detect neutrino-portal dark matter via a specialized neutrino detector, leveraging well-understood muon decay neutrino fluxes to improve search sensitivity for neutrinophilic mediators.

Contribution

It proposes a novel neutrino detector setup near a muon collider and demonstrates its enhanced capability to search for neutrino-portal dark matter and neutrinophilic mediators in the MeV to GeV mass range.

Findings

MuColν can surpass other methods in detecting neutrinophilic mediators.

The detector is effective with only 10 kg-yr exposure.

It can probe thermal freeze-out and freeze-in dark matter models.

Abstract

With no concrete evidence for non-gravitational interactions of dark matter to date, it is natural to wonder whether dark matter couples predominantly to the Standard Model (SM)'s neutrinos. Neutrino interactions (and the possible existence of additional neutrinophilic mediators) are substantially less understood than those of other SM particles, yet this picture will change dramatically in the coming decades with new neutrino sources. One potential new source arises with the construction of a high-energy muon collider (MuCol) -- due to muons' instability, a MuCol is a source of high-energy collimated neutrinos. Importantly, since the physics of muon decays (into neutrinos) is very well-understood, this leads to a neutrino flux with systematic uncertainties far smaller than fluxes from conventional high-energy (proton-sourced) neutrino beams. In this work, we study the capabilities of a potential neutrino detector, "MuCol$\nu$," placed ~100 m downstream of the MuCol interaction point. The MuCol$\nu$ detector would be especially capable of searching for a neutrinophilic mediator $\phi$ through the mono-neutrino scattering process $\nu_\mu N \to \mu^+ \phi X$, exceeding searches from other terrestrial approaches for $m_\phi$ in the ~few MeV -- ten GeV range. Even with a 10 kg-yr exposure, MuCol$\nu$ is capable of searching for well-motivated classes of thermal freeze-out and freeze-in neutrino-portal dark matter.