Probing the dark sector with nuclear transition photons

TL;DR

This paper demonstrates that nuclear transition photon detection in existing neutrino detector data provides a highly sensitive method for probing light dark matter, surpassing previous elastic scattering searches and covering a wide mass range.

Contribution

It introduces a novel detection channel via nuclear excitation decay, significantly improving sensitivity to light dark matter in beam-dump experiments.

Findings

Set world-leading constraints on scalar dark-photon portal models.

Demonstrated sensitivity to the thermal relic abundance benchmark.

Future experiments could extend this sensitivity to fermionic dark matter.

Abstract

Here we present world-leading sensitivity to light ($< 170$ MeV) dark matter (DM) using beam-dump experiments. Dark sector particles produced during pion decay at accelerator beam-dumps can be detected via scattering in neutrino detectors. The decay of nuclei excited by the inelastic scattering of DM is an unexploited channel which has significantly better sensitivity than similar searches using the elastic scattering channel. We show that this channel is a powerful probe of DM by demonstrating sensitivity to the thermal relic abundance benchmark in a scalar DM dark-photon portal model. This is achieved through the use of existing data, obtained by the KARMEN experiment over two decades ago, which allow us to set world-leading constraints on this model over a wide mass range. With experimental improvements planned for the future, this technique will be able to probe the thermal relic benchmark for fermionic DM across a wide mass range.