Probing Sub-MeV Dark Matter with Neutron-Capture $\gamma$ Spectroscopy

TL;DR

This paper introduces a new spectroscopy method using correlated gamma-ray lines to search for weakly coupled particles emitted during neutron capture, improving detection sensitivity and reducing background ambiguities.

Contribution

The paper develops a general framework leveraging satellite-line combs and likelihood analysis for detecting new particles in nuclear de-excitation, enhancing previous techniques.

Findings

Method suppresses nuclear-structure ambiguities.

Combines data across multiple nuclei for stronger signals.

Applicable with high-resolution HPGe detectors.

Abstract

We present a general, discovery-grade framework for searching for weakly coupled new particles emitted in nuclear de-excitation following neutron capture. Rather than relying on isolated spectral features, the method exploits correlated ``satellite-line combs'': multiple weak $\gamma$-ray lines appearing at a common energy offset $\Delta$ below known capture transitions. By combining likelihood information across many parent lines and multiple target nuclei, the approach strongly suppresses nuclear-structure ambiguities and instrumental artifacts. We also discuss optimal target selection and practical experimental implementation with high-resolution HPGe detectors.