Exploring Low-Mass Dark Matter with CRESST

Abstract

The CRESST-II (Cryogenic Rare Event Search with Superconducting Thermometers) experiment, whose second phase has been successfully finished in summer 2015, aims at the direct detection of dark matter particles. The intrinsic radiopurity of CaWO 4 crystals, the capability to reject recoil events from alpha-surface contamination, and the energy threshold were significantly improved compared to previous runs of the experiment. A moderate exposure of 29 kg-days acquired by one ∼250 g CaWO 4 detector provides competitive limits on the spin-independent dark matter particle-nucleon cross section and probes a new region of parameter space for dark matter particle masses below 3 GeV/c 2 . The potential for low-mass dark matter particle search can be further exploited by a new detector design planned for CRESST-III. We describe the experimental strategy for the near future and give projections for the sensitivity.

Dark Matter Detection Using Helium Evaporation and Field Ionization

“…Finally, a solid crystalline target offers a means to further reduce the threshold phonon energy required to evaporate helium atoms. 4 He is very weakly bound to the alkali metals, with an adsorption energy ranging from 1.2 meV for lithium [56] to 0.33 meV for cesium [57][58][59]. The binding energy for 3 He is even less, being only 0.17 meV on cesium [60].…”

“…Recently, a number of theoretical models have been proposed in which the mass m χ of dark matter particles would be below ∼ 10 GeV/c 2 , and thus below the mass range that can be easily detected in most of the current experiments [3]. In the search for low mass dark matter particles by direct detection, the energy threshold of the detector is the key parameter [4,5]. Present techniques based on electronic excitations of semiconductors [6][7][8][9], scintillation from transparent crystals [4,5], and/or the thermal response of the target by sensitive thermometers [4-6, 8, 9] all require the deposition of about 1 eV or more.…”

“…In the search for low mass dark matter particles by direct detection, the energy threshold of the detector is the key parameter [4,5]. Present techniques based on electronic excitations of semiconductors [6][7][8][9], scintillation from transparent crystals [4,5], and/or the thermal response of the target by sensitive thermometers [4-6, 8, 9] all require the deposition of about 1 eV or more. Various techniques such as the use of narrow gap semiconductors [10,11] or superconductors [12] have been suggested to lower this energy threshold.…”

“…1a. When the temperature is below 100 mK, the equilibrium density of 4 He in the vapor phase is below 10 −12 cm −3 and the number of thermal rotons in the liquid is negligible. A helium recoil results in a complex string of processes, but the final outcome is the production of phonon and roton excitations [22].…”

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

“…The experiment was optimized for the measurement of QF W [25,33]. To enhance the number of W-scatters a scattering angle of Θ = 80 • was chosen due to scattering kinematics [27].…”