Dark sectors in neutron-shining-through-a-wall and nuclear absorption signals

TL;DR

This paper proposes new experimental approaches to detect dark neutrons through neutron-shining-through-a-wall signals and nuclear absorption, providing stronger constraints on dark baryon mixing and dark matter interactions.

Contribution

It introduces novel search strategies using existing neutrino detectors and explores the implications of dark neutrons as dark matter, enhancing current experimental constraints.

Findings

IsoDAR can detect $n o n'$ transitions with low background.

Nuclear absorption in underground detectors constrains dark neutron parameters.

Additional signatures include neutron disappearance and wall-shining at various sources.

Abstract

We propose new searches for $n^\prime$, a dark baryon that can mix with the Standard Model neutron. We show that IsoDAR, a proposal to place an intense cyclotron near a large-volume neutrino detector deep underground, can look for $n\to n^\prime \to n$ transitions with much lower backgrounds than surface experiments. This opportune neutron-shining-through-a-wall search would be possible without any modifications to the primary goals of the experiment and would provide the strongest laboratory constraints on the $n$-$n^\prime$ mixing for a wide range of mass splitting. We also consider dark neutrons as dark matter and show that their nuclear absorption at deep-underground detectors such as SNO and Borexino places some of the strongest limits in parameter space. Finally, we describe other $n^\prime$ signatures, such as neutrons shining through walls at spallation sources, reactors, and the disappearance of ultracold neutrons.