Pulse shape discrimination for the CONUS experiment in the keV and sub-keV regime

Abstract

Point-contact p-type high-purity germanium detectors (PPC HPGe) are particularly suited for detection of sub-keV nuclear recoils from coherent elastic scattering of neutrinos or light dark matter particles. While these particles are expected to interact homogeneously in the entire detector volume, specific classes of external background radiation preferably deposit their energy close to the semi-active detector surface, in which diffusion processes dominate that subsequently lead to slower rising pulses compared to the ones from the fully active bulk volume. Dedicated studies of their shape are therefore highly beneficial for the understanding and the rejection of these unwanted events. This article reports about the development of a data-driven pulse shape discrimination (PSD) method for the four 1 kg size PPC HPGe detectors of the CONUS experiment in the keV and sub-keV regime down to 210 eV${}_{\text{ee}}$. The impact of the electronic noise at such low energies is carefully examined. It is shown that for an acceptance of 90% of the faster signal-like pulses from the bulk volume, approx. 50% of the surface events can be rejected at the energy threshold and that their contribution is fully suppressed above 800 eV${}_{\text{ee}}$. Applied to the CONUS background data, such a PSD rejection cut allows to achieve an overall (15-25)% reduction of the total background budget. The new method allows to improve the sensitivity of future CONUS analyses and to refine the corresponding background model in the sub-keV energy region.

References in corpus (9)

• Constraints on elastic neutrino nucleus scattering in the fully coherent regime from the CONUS experiment
• Direct measurement of the ionization quenching factor of nuclear recoils in germanium in the keV energy range
• Optimizing EDELWEISS detectors for low-mass WIMP searches
• First results from a search for coherent elastic neutrino-nucleus scattering (CE$\nu$NS) at a reactor site
• First upper limits on neutrino electromagnetic properties from the CONUS experiment
• Multi-site event discrimination for the MAJORANA DEMONSTRATOR
• Pulse shape analysis in GERDA Phase II
• Full background decomposition of the CONUS experiment
• Identification of the anomalous fast bulk events in a p-type point contact germanium detector

Cited by in corpus (7)

• Direct observation of coherent elastic antineutrino-nucleus scattering
• New Limits on Coherent Neutrino Nucleus Elastic Scattering Cross Section at the Kuo-Sheng Reactor Neutrino Laboratory
• Final CONUS results on coherent elastic neutrino-nucleus scattering at the Brokdorf reactor
• New constraints on coherent elastic neutrino-nucleus scattering by the nuGeN experiment
• Light vector bosons and the weak mixing angle in the light of future germanium-based reactor CE$\nu$NS experiments
• Bulk-Surface Event Discrimination in Point Contact Germanium Detectors at Near-Threshold Energies with Shape-Matching Pulse-Shape Methods
• Estimation of waveform deformation with the matched filter