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

Fornal and Grinstein(1) propose that the discrepancy between the beam and bottle methods of neutron lifetime measurements can be explained by a previously unobserved dark matter decay mode n$\rightarrow$γ+X.  We have performed a search for this decay mode over the allowed range of energies of the monoenergetic gamma ray (2). In this recent work, a Compton-suppressed high-purity germanium detector was used to identify γ-rays from the decay of ultra-cold neutrons (UCNs) stored in a nickel-phosphorous coated stainless-steel bottle. The possibility of a sufficiently strong branch to explain the lifetime discrepancy was excluded with 97% confidence. Setup for a new experiment with a factor of 5 improved gamma ray resolution, and about two times higher UCN density. Results with approximately 5 times higher sensitivity will be presented.

1. Fornal B, Grinstein B. "Dark Matter Interpretation of the Neutron Decay Anomaly". Phys. Rev. Lett. 120, 191801 (2018).

2. Tang Z, Blatnik M, Broussard L, Choi J, Clayton S, Cude-Woods C, et al. Search for the Neutron Decay n $\rightarrow $ X+ $\gamma $ where X is a dark matter particle. arXiv preprint arXiv:180201595. 2018.