CRESST III Phase 1

The goal of CRESST-III is to further increase the sensitivity of the experiment - especially for low dark matter particle masses. Therefore, the mass of the detector crystals was reduced by a factor of about 10 to 24g. In this way, detector thresholds below 100eV can be achieved.

On the left an opened CRESST-III detector module can be seen. Both, the block-shaped CaWO₄ detector crystal as well as the SOS light detector are held by CaWO₄ sticks to ensure a fully scintillating housing surrounding the detectors. On the right, a heat pulse with an energy of 500eV recorded by such a detector is shown.

Since November 2016, the experiment is steadily collecting dark matter data. A first analysis was performed for one detector module (Det-A) which shows the best overall performance of all modules operated in CRESST-III Phase 1. Altough the energy threshold of Det-A is even lower than 50eV, a conservative analysis threshold of 100eV was chosen for this analysis. The analysis and its results are described here .

The light yield-energy plane of Det-A including raw data with an exposure of 2.39 kg days is shown in the following figure:

The blue lines mark the 90% upper and lower boundaries of the electron/gamma band. The nuclear recoil bands are drawn in red (oxygen) and green (tungsten). The acceptance region marked in yellow extends in energy between the analysis threshold of 100eV and 40keV. In light yield it is limited by the 99.5% lower boundary of the tungsten band and by the center of the oxygen band.

The resulting exclusion limit (drawn as solid red line) calculated with the Yellin optimum interval method extends for the first time down to dark matter particle masses of 350 MeV/c^2. At 500 MeV/c^2 the limit is improved by one order of magnitude, while for higher masses it is comparable to the 2016 result (red dashed line, see CRESST-II Phase 2 ), despite of the much smaller exposure.


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