Energy-dependent light quenching in CaWO $$_4$$ 4 crystals at mK temperatures

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 QF ROI O = (11.2 ± 0.5) %, QF ROI Ca = (5.94±0.49) % and QF ROI W = (1.72±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 previa

Exploring Low-Mass Dark Matter with CRESST

“…Due to light quenching [12] in CaWO 4 , the scintillation light detection allows to identify the type of particle interaction. This is crucial to discriminate unavoidable beta/gamma backgrounds from possible dark matter particle-induced nuclear-recoil events which, to a certain extent, can be even tagged as O, Ca, and W recoils [13].…”

Exploring $$\hbox {CE}\nu \hbox {NS}$$ with NUCLEUS at the Chooz nuclear power plant

“…For example, in case of a cubic muon-veto of 1 m side length with a count rate of R = (487 ± 38) Hz the pulse's onset has to be determined with σ τ 20 µs to restrict the dead time to 10%. The precision of the pulse onset of a fast cryogenic detector with a rise time of 100 µs has been measured using a pulsed neutron beam from an accelerator in [44]. The uncertainty of the onset determination is σ τ = (4.8 ± 0.4) µs corresponding to a time window of 48 µs around every event in the muon-veto to be removed from the exposure time.…”

TES-Based Light Detectors for the CRESST Direct Dark Matter Search

“…α particles have a reduced light output (LY around 20%). The more massive recoiling nuclei cause a further reduced scintillation output with light yields of 11% (O), 6% (Ca), 2% (W) relative to electron-recoil events [3]. Figure 1 shows a typical plot of LY versus phonon energy obtained in a neutron calibration during CRESST-II.…”

“…The magenta lines show the 90% upper bound of the oxygen-recoil band and the 90% lower bound of the tungsten band. The mean of the electron-recoil band turns below one at small energies due to scintillator non-proportionality [3]. A population of events above the electron-recoil band, called excess-light events, is attributed to external radiation emitting additional light in the scintillating foil [4] (Color figure online) detector resolution yields a more precise measurement of the LY, resulting in narrower bands.…”