The SWEET project: probing sugar crystals for direct dark matter searches

TL;DR

The paper addresses the challenge of detecting sub-GeV/$c^2$ dark matter by leveraging hydrogen-rich organic targets, proposing sucrose as a promising absorber for direct detection. It presents the first results from a sucrose monocrystal operated at milliKelvin temperatures with phonon and scintillation readout, including the detector design and initial observations of scintillation through coincident heat and light signals. The study demonstrates that sugar crystals can function as cryogenic calorimeters and points to further improvements—larger, purer crystals and TES-based readout—to push sensitivity toward sub-GeV DM, potentially expanding the reach of direct detection. Overall, the SWEET project opens a new avenue for organic-crystal detectors in the low-mass dark matter parameter space, with implications for both spin-independent and spin-dependent interactions; the analysis employs a standard halo model with $ ho_{DM} = 0.3$ GeV/(c$^2$ cm$^3$) and typical WIMP velocity benchmarks to project limits.

Abstract

Several experiments searching for direct dark matter interactions aim to achieve unprecedented sensitivity to sub-GeV/c$^2$ dark matter masses through elastic scattering with nuclei in various target crystals at cryogenic temperatures. Hydrogen-rich materials, such as organic compounds, are promising candidates for the detection of sub-GeV/c$^2$ dark matter due to favourable kinematics. In this paper, we present for the first time results obtained with a sugar-based phonon detector employing sucrose crystals ($\mathbf{C_{12}H_{22}O_{11}}$), capable of particle detection with associated scintillation light.

Figures (6)

• Figure 1: Projected dark matter exclusion limits for sapphire, calcium tungstate, helium, lithium aluminate, carbon, and sucrose, under the assumptions outlined in the text.
• Figure 2: (a) Initial sugar crystallization on a suspended nylon wire immersed in the supersaturated solution; (b) Sugar crystals formed after several weeks of slow recrystallization. An example of a monocrystalline crystal is indicated in the circle; (c) Sugar crystals collected from the supersaturated solution. The crystal highlighted in the circle was selected for the prototype detector described in this work.
• Figure 3: (a) Sugar crystal instrumented with an NTD thermistor and mounted in its copper holder. Larger sugar crystals, produced using the same procedure, are visible in the box below the detector; (b) Light detector module mounted above the sugar detector.
• Figure 4: Spectrum of filtered pulses obtained from the sugar detector after applying the optimum filter to the triggered events.
• Figure 5: Example of coincident events detected simultaneously in the sugar and the light detector.