Abstract
Scintillating CaWO $$_4$$ single crystals are a promising multi-element target for rare-event searches and are currently used in the direct dark matter experiment CRESST (Cryogenic Rare Event Search with Superconducting Thermometers). The relative light output of different particle interactions in CaWO $$_4$$ is quantified by quenching factors (QFs). These are essential for an active background discrimination and the identification of a possible signal induced by weakly interacting massive particles (WIMPs). We present the first precise measurements of the QFs of O, Ca and W at mK temperatures by irradiating a cryogenic detector with a fast neutron beam. A clear energy dependence of the QF of O and, less pronounced, of Ca was observed for the first time. Furthermore, in CRESST neutron-calibration data a variation of the QFs among different CaWO $$_4$$ single crystals was found. For typical CRESST detectors the QFs in the region-of-interest (10–40 keV) are $$\hbox {QF}_\mathrm{O}^\mathrm{ROI}=(11.2\pm 0.5)$$ %, $$\hbox {QF}_\mathrm{Ca}^\mathrm{ROI}=(5.94\pm 0.49)$$ % and $$\hbox {QF}_\mathrm{W}^\mathrm{ROI}=(1.72\pm 0.21)$$ %. The latest CRESST data (run32) is reanalyzed using these fundamentally new results on light quenching in CaWO $$_4$$ having moderate influence on the WIMP analysis. Their relevance for future CRESST runs and for the clarification of previously published results of direct dark matter experiments is emphasised.
Highlights
Rare-event searches for dark matter (DM) in the form of weakly interacting massive particles (WIMPs) [1,2] have reached impressive sensitivities during the last decade [3]
While QFO clearly rises towards lower recoil energies, this effect is less pronounced for QFCa
A correlated ML fit was performed based on the following assumptions: (1) for the mean LY of O- and Ca-scatters the phenomenological parametrization LYx (Er ) = LY∞x (1 + fx · exp (−Er /λx )) is proposed with the free parameters LY∞x (LY at Er = ∞), fx and λx, and (2) the mean LY of W-scatters is approximated to be constant in the relevant energy range at the value precisely measured with the triple-coincidence technique (LYW = 0.0208 ± 0.0024 which corresponds to QFW = (1.96 ± 0.22) %)
Summary
Rare-event searches for dark matter (DM) in the form of weakly interacting massive particles (WIMPs) [1,2] have reached impressive sensitivities during the last decade [3]. While the DAMA/LIBRA [5], and recently the CoGeNT [6], CRESST [7] and the CDMS(Si) [8] experiments observed excess signals that might be interpreted as induced by DM particles with mχ ∼ 10 GeV/c2 at WIMP–nucleon cross sections of ∼10−4 pb, this scenario is ruled out by the LUX [9] and XENON100 [10] experiments, and almost excluded by the CDMS(Ge) [11,12], the EDELWEISS [13,14] and the SuperCDMS [15] experiments.
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