Beta/gamma and alpha backgrounds in CRESST-II Phase 2

Abstract

The experiment CRESST-II aims at the detection of dark matter with scintillating CaWO${}_4$ crystals operated as cryogenic detectors. Recent results on spin-independent WIMP-nucleon scattering from the CRESST-II Phase 2 allowed to probe a new region of parameter space for WIMP masses below 3 GeV/c${}^2$. This sensitivity was achieved after background levels were reduced significantly. We present extensive background studies of a CaWO${}_4$ crystal, called TUM40, grown at the Technische Universität München. The average beta/gamma rate of 3.51/[kg keV day] (1-40 keV) and the total intrinsic alpha activity from natural decay chains of $3.08\pm 0.04$ mBq/kg are the lowest reported for CaWO${}_4$ detectors. Contributions from cosmogenic activation, surface-alpha decays, external radiation and intrinsic alpha/beta emitters are investigated in detail. A Monte-Carlo based background decomposition allows to identify the origin of the majority of beta/gamma events in the energy region relevant for dark matter search.

17 pages, 7 figures, 3 tables

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• Energy-Dependent Light Quenching in CaWO${}_4$ Crystals at mK Temperatures
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Cited by in corpus (15)

• First results from the CRESST-III low-mass dark matter program
• The $\nu$-cleus experiment: A gram-scale fiducial-volume cryogenic detector for the first detection of coherent neutrino-nucleus scattering
• EXCESS workshop: Descriptions of rising low-energy spectra
• Gram-scale cryogenic calorimeters for rare-event searches
• Annual Modulation in Direct Dark Matter Searches
• Cosmogenic activation of materials
• A prototype detector for the CRESST-III low-mass dark matter search
• Radioactive contamination of scintillators
• A detector module with highly efficient surface-alpha event rejection operated in CRESST-II Phase 2
• Dark-Photon Search using Data from CRESST-II Phase 2
• Radiopurity of a kg-scale PbWO${}_4$ cryogenic detector produced from archaeological Pb for the RES-NOVA experiment
• Limits on momentum-dependent asymmetric dark matter with CRESST-II
• Cosmogenic activation in double beta decay experiments
• Cryogenic phonon-scintillation detectors with PMT readout for rare event search experiments
• High-Dimensional Bayesian Likelihood Normalisation for CRESST's Background Model