Search for the Neutron Decay n$\rightarrow$ X+$\gamma$ where X is a dark matter particle

TL;DR

This study searches for a hypothesized neutron decay into a dark matter particle and a gamma ray, aiming to explain neutron lifetime measurement discrepancies, but finds no evidence for such decay at significant levels.

Contribution

The paper provides the first experimental search over the gamma ray energy range for the proposed dark matter decay mode of the neutron, excluding its role in the lifetime discrepancy.

Findings

No evidence of the decay mode at >4 sigma confidence.

Constraints on the decay branching ratio are established.

The dark matter decay hypothesis cannot fully explain the neutron lifetime discrepancy.

Abstract

In a recent paper submitted to Physical Review Letters, Fornal and Grinstein have suggested that the discrepancy between two different methods of neutron lifetime measurements, the beam and bottle methods can be explained by a previously unobserved dark matter decay mode, n$\rightarrow$ X+$\gamma$ where X is a dark matter particle. We have performed a search for this decay mode over the allowed range of energies of the monoenergetic gamma ray for X to be a dark matter particle. We exclude the possibility of a sufficiently strong branch to explain the lifetime discrepancy with greater than 4 sigma confidence.