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Register a new userDeep learning based pulse shape discrimination for germanium detectors
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Experiments searching for rare processes like neutrinoless double beta decay heavily rely on the identification of background events to reduce their background level and increase their sensitivity. We present a novel machine learning based method to recognize one of the most abundant classes of background events in these experiments. By combining a neural network for feature extraction with a smaller classification network, our method can be trained with only a small number of labeled events. To validate our method, we use signals from a broad-energy germanium detector irradiated with a $^{228}$Th gamma source. We find that it matches the performance of state-of-the-art algorithms commonly used for this detector type. However, it requires less tuning and calibration and shows potential to identify certain types of background events missed by other methods.
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We report on the characterization of two inverted coaxial Ge detectors in the context of being employed in future $^{76}$Ge neutrinoless double beta ($0 ubetabeta$) decay experiments. It is an advantage that such detectors can be produced with bigger Ge mass as compared to the planar Broad Energy Ge detectors (BEGe) that are currently used in the GERDA $0 ubetabeta$ decay experiment. This will result in lower background for the search of $0 ubetabeta$ decay due to a reduction of cables, electronics and holders. The measured resolution near the $^{76}$Ge Q-value at 2039 keV is 2.5 keV and their pulse-shape characteristics are similar to BEGe-detectors. It is concluded that this type of Ge-detector is suitable for usage in $^{76}$Ge $0 ubetabeta$ decay experiments.
Using the waveforms from a digital electronic system, an offline analysis technique on pulse shape discrimination (PSD) has been developed to improve the neutron-gamma separation in a bar-shaped NE-213 scintillator that couples to a photomultiplier tube (PMT) at each end. The new improved method, called the ``valued-assigned PSD (VPSD), assigns a normalized fitting residual to every waveform as the PSD value. This procedure then facilitates the incorporation of longitudinal position dependence of the scintillator, which further enhances the PSD capability of the detector system. In this paper, we use radiation emitted from an AmBe neutron source to demonstrate that the resulting neutron-gamma identification has been much improved when compared to the traditional technique that uses the geometric mean of light outputs from both PMTs. The new method has also been modified and applied to a recent experiment at the National Superconducting Cyclotron Laboratory (NSCL) that uses an analog electronic system.
In a dedicated test setup at the Kamioka Observatory we studied pulse shape discrimination (PSD) in liquid xenon (LXe) for dark matter searches. PSD in LXe was based on the observation that scintillation light from electron events was emitted over a longer period of time than that of nuclear recoil events, and our method used a simple ratio of early to total scintillation light emission in a single scintillation event. Requiring an efficiency of 50% for nuclear recoil retention we reduced the electron background to 7.7pm1.1(stat)pm1.2 0.6(sys)times10-2 at energies between 4.8 and 7.2 keVee and to 7.7pm2.8(stat)pm2.5 2.8(sys)times10-3 at energies between 9.6 and 12 keVee for a scintillation light yield of 20.9 p.e./keV. Further study was done by masking some of that light to reduce this yield to 4.6 p.e./keV, the same method results in an electron event reduction of 2.4pm0.2(stat)pm0.3 0.2(sys)times10-1 for the lower of the energy regions above. We also observe that in contrast to nuclear recoils the fluctuations in our early to total ratio for electron events are larger than expected from statistical fluctuations.
A new package to simulate the formation of electrical pulses in segmented true-coaxial high purity germanium detectors is presented. The computation of the electric field and weighting potentials inside the detector as well as of the trajectories of the charge carriers is described. In addition, the treatment of bandwidth limitations and noise are discussed. Comparison of simulated to measured pulses, obtained from an 18-fold segmented detector operated inside a cryogenic test facility, are presented.
We measured the decay time of the scintillation pulses produced by electron and nuclear recoils in CaF2(Eu) by a new fitting method. In the recoil energy region 5-30 keVee, we found differences of the decay time between electron and nuclear recoil events. In the recoil energy region above 20 keVee, we found that the decay time is independent of the recoil energy.
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