Speaker
Description
We discovered event-by-event identification of nuclear recoils in silicon from the spatial correlation between the primary ionization event and the defect cluster left behind by the recoiling atom, later identified as a localized excess of leakage current under thermal stimulation. By irradiating a charge-coupled device (CCD) with an AmBe neutron source, we demonstrate full efficiency in the identification of nuclear recoils down to 90 keV, decreasing to 50% at 8 keV and reaching (6$\pm$2)% between 1.5 and 3.5 keV. Irradiation with a $^{24}$Na $\gamma$-ray source does not result in any detectable defect clusters. This is the first realization of nuclear/electronic recoil discrimination in CCDs, a leading technology in direct searches for dark matter. We present our plans to extend the technique to sub-keV nuclear recoils, which will greatly improve the sensitivity of the upcoming kg-scale CCD experiments to dark matter-nucleus interactions.
