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16-06-15

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

Authors: R. Strauss et al.
Group: CRESST
Category: Reviewed Paper

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 $3\,\mathrm{GeV/c^2}$. This sensitivity was achieved after background levels were reduced significantly. We present extensive background studies of a $\mathrm{CaWO_4}$ crystal, called TUM40, grown at the Technische Universit\"at M\"unchen. The average beta/gamma rate of $3.44/\mathrm{[kg\,keV\,day]}$ ($1-40\,\mathrm{keV}$) and the total intrinsic alpha activity from natural decay chains of $3.08\pm0.04\,\mathrm{mBq/kg}$ are the lowest reported for \mathrm{CaWO_4}$ detectors. Contributions of gamma lines resulting from cosmogenic activation, external X-rays and intrinsic beta emitters are investigated in detail.