First observation of isolated nuclear recoils following neutron capture for dark matter calibration

TL;DR

This study reports the first detection of isolated nuclear recoils caused by neutron capture in silicon, demonstrating a new calibration method for low-energy nuclear recoils relevant to dark matter detection.

Contribution

It introduces the observation of neutron capture-induced nuclear recoils at very low energies, advancing calibration techniques for dark matter and neutrino experiments.

Findings

Detection of neutron capture-induced nuclear recoils at 450 eV

Improved fit with capture recoil model supports the observation

Thermal neutron calibration shows promise for low-energy recoil measurements

Abstract

Low-energy nuclear recoils (NRs) are hard to measure because they produce few e$^{-}$/h$^+$ pairs in solids -- i.e. they have low "ionization yield". A silicon detector was exposed to thermal neutrons over 2.5\,live-days, probing NRs down to 450\,eV. The observation of a neutron capture-induced component of NRs at low energies is supported by the much-improved fit upon inclusion of a capture NR model. This result shows that thermal neutron calibration of very low recoil energy NRs is promising for dark matter searches, coherent neutrino experiments, and improving understanding of ionization dynamics in solids.