Results on MeV-scale dark matter from a gram-scale cryogenic calorimeter operated above ground

Abstract: Models for light dark matter particles with masses below 1 GeV/c$^2$ are a natural and well-motivated alternative to so-far unobserved weakly interacting massive particles. Gram-scale cryogenic calorimeters provide the required detector performance to detect these particles and extend the direct dark matter search program of CRESST. A prototype 0.5 g sapphire detector developed for the $\nu$-cleus experiment has achieved an energy threshold of $E_{th}=(19.7\pm 0.9)$ eV, which is one order of magnitude lower than previous results and independent of the type of particle interaction. The result presented here is obtained in a setup above ground without significant shielding against ambient and cosmogenic radiation. Although operated in a high-background environment, the detector probes a new range of light-mass dark matter particles previously not accessible by direct searches. We report the first limit on the spin-independent dark matter particle-nucleon cross section for masses between 140 MeV/c$^2$ and 500 MeV/c$^2$.

Insights into MeV-scale Dark Matter Detection via Cryogenic Calorimetry

The paper presents novel results from the operation of a gram-scale cryogenic calorimeter above ground, targeting MeV-scale dark matter (DM). The CRESST collaboration offers a noteworthy advancement in the direct detection of DM particles, focusing on masses below 1 GeV/c². Leveraging the capabilities of a 0.5 g sapphire detector, initially devised for the $\nu$-cleus experiment, the study achieves an unprecedented energy threshold of approximately 19.7 eV, surpassing previous benchmarks by an order of magnitude.

Key Advances and Methodological Innovations

Cryogenic calorimeters are distinguished by their ability to detect temperature fluctuations induced by particle interactions, proving adept at capturing elusive low-energy signals pertinent to DM searches. The detector developed employs transition-edge sensors (TES) on sapphire crystals, optimizing non-thermal phonon sensitivity. Its compact size and enhanced sensitivity enable the exploration of new DM mass ranges, demonstrating technical sophistication and effective application of TES technology in particle physics.

Crucially, the detector operated without significant shielding against environmental radiation, yet effectively maintained its minimal threshold, highlighting its robustness in a high-background context. This capability permits direct probing of DM particle-nucleus interactions at masses previously inaccessible to direct search experiments, specifically between 140 MeV/c² and 500 MeV/c².

Analytical Results and Implications

The results extend the spin-independent cross-section measurements for DM-nucleon interactions into novel territories. The presented limits fill a gap left by traditional searches predominantly focusing on heavier, weakly interacting massive particles (WIMPs). By correlating direct detection data with recoil spectra calculations, the study delineates constraints that rival, and potentially exceed, those derived from alternative methods like bremsstrahlung emission detection.

Such advancements offer pivotal insights into DM models that deviate from conventional WIMPs, encompassing light DM theories involving asymmetric, scalar, or hidden sector particles. These models are promising and theoretically compelling, aligning with observational constraints on relic density and the cosmological overclosure problem.

Prospective Developments in Dark Matter Research

The implications of this research are manifold. Firstly, it demonstrably broadens the scope of particle physics experiments, underscoring the potential of cryogenic calorimetry to shift paradigms in DM detection. Secondly, the methodological rigor illustrated in managing and interpreting high-background measurements above ground signals significant promise for future surface or shallow underground installations.

Future trajectories in MeV-scale DM research can build upon these findings, capitalizing on enhanced detector sensitivity and reduced background environments. The ongoing development hinted by the collaboration suggests imminent technological refinement, potentially ushering in sensitivity thresholds reaching single-digit eV levels. This refinement could catalyze breakthroughs in identifying lighter DM candidates and broaden theoretical exploration within DM research.

In conclusion, the paper contributes substantial empirical data within the DM search domain, reinforcing the viability of cryogenic calorimeters as valuable instruments in unveiling the complexities of dark matter. Through meticulous analysis and strategic deployment of sophisticated detector technology, the study sets a precedent for innovative exploration at the frontier of particle physics.