Ionization measurement at very low temperature for nuclear and electron recoils discrimination by ionization-heat simultaneous measurement for dark matter research

To achieve a high level of discrimination between nuclear recoils and electron recoils for dark matter research, we realized and studied ionization-heat detectors working at very low temperature (10–20 mK). To understand the mechanisms underlying the ionization measurement at this temperature range, we made systematic studies of detectors performances (time stability, energy resolution, etc.) in X- and γ-rays detection for Ge and Si detectors. Results are presented and discussed. We found that the time stability is governed by the progressive space charge build-up due to impurities ionization by far-infrared radiation. Moreover if the energy resolution of HPGe-pin detectors is limited by the noise, it appears to be intrinsically limited by carrier trapping on neutral impurities in Si detectors.