First germanium-based constraints on sub-MeV Dark Matter with the EDELWEISS experiment (2003.01046v2)

Abstract: The EDELWEISS collaboration has performed a search for Dark Matter (DM) particles interacting with electrons using a 33.4 g Ge cryogenic detector operated underground at the LSM. A charge resolution of 0.53 electron-hole pairs (RMS) has been achieved using the Neganov-Trofimov-Luke amplification with a bias of 78 V. We set the first Ge-based constraints on sub-MeV/c$^{2}$ DM particles interacting with electrons, as well as on dark photons down to 1 eV/c$^2$. These are competitive with other searches. In particular, new limits are set on the kinetic mixing of dark photon DM in a so far unconstrained parameter space region in the 6 to 9 eV/c$^2$ mass range. These results demonstrate the high relevance of cryogenic Ge detectors for the search of DM interactions producing eV-scale electron signals.

• The paper demonstrates the first germanium-based constraints on sub-MeV dark matter using a 33.4 g cryogenic detector at LSM.
• The experiment leverages the Neganov-Trofimov-Luke effect to achieve a 0.53 electron-hole pair resolution, enhancing sensitivity to low-energy signals.
• The findings extend the dark matter parameter space by setting limits on dark photons down to 1 eV/c², guiding future detector improvements.

Insights into Sub-MeV Dark Matter Searches via Germanium Detectors in the EDELWEISS Experiment

The paper "First germanium-based constraints on sub-MeV Dark Matter with the EDELWEISS experiment" introduces significant findings from the EDELWEISS collaboration, focusing on the search for Dark Matter (DM) particles by leveraging a cryogenic germanium detector. This research contributes to the understanding of Dark Matter interactions with electrons, particularly in the sub-MeV/c² mass range, and explores potential interactions with dark photons.

Experimental Design and Achievements

The EDELWEISS collaboration utilized a cryogenic detector made of 33.4 g of germanium, which was operated underground at the Laboratoire Souterrain de Modane (LSM). Notable is the adoption of the Neganov-Trofimov-Luke (NTL) effect, which, when a bias of 78 V was applied, led to a charge resolution of 0.53 electron-hole pairs root mean square (RMS). This methodological approach leverages the increased energy sensitivity provided by the smaller band-gap energy of germanium compared to silicon, thus enhancing sensitivity to lighter DM particles.

Results and Data Interpretation

The achieved results set the first germanium-based constraints on DM particles below a MeV/c² mass, as well as limits on dark photons down to 1 eV/c². Specifically, within the mass range of 6 to 9 eV/c², the constraints on the kinetic mixing parameter $\kappa$ for dark photons penetrate previously unexplored regions. The detector's ability to resolve single electron-hole pairs and effectively measure such small energy deposits has significant implications for expanding DM detection capabilities in the sub-MeV mass range.

The researchers performed data collection and analysis under controlled conditions, using a sequence of tests to determine efficiency and resolution. The limitations were identified, such as the occurrence of "heat-only" events not attributable to NTL amplification, which constrains detection above certain energy thresholds. Nevertheless, this work represents an advancement in improving single electron-hole pair resolution.

Implications for Dark Matter Research

The implications of these findings are multifold. Practically, the techniques and technology used by the EDELWEISS collaboration demonstrate the potential of cryogenic germanium detectors as robust tools in the DM search, particularly in probing interactions that generate eV-scale electron signals. From a theoretical perspective, the results suggest alternative parameter spaces and interaction models for DM that merit further investigation.

Future Developments and Considerations

In the context of the EDELWEISS-SubGeV program, this paper signifies a promising step forward in utilizing cryogenic semiconductor technology for DM searches. Looking forward, planned advancements include improved detector energy resolution through upgraded electronics and further refined sensor technologies. The team is also exploring electrode configurations that potentially offer enhanced sensitivity.

The integration of Superconducting Single-Photon Detectors (SSPD) is under consideration to improve discrimination capabilities against heat-only backgrounds. Such technological progress and the continual adaptation of germanium-based detectors promise to enhance the detection of light DM particles, pushing the boundaries of DM direct detection experiments.

In summary, this paper presents critical experimental results and sets the groundwork for further exploration in DM research, reinforcing the relevance of cryogenic germanium detectors in developing a coherent understanding of DM interactions across a breadth of unexplored mass ranges.