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

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