DAMIC-M is a complex detector which integrates an innovative technology into an apparatus with stringent constraints on radioactive contaminants. Major achievements during the time of the project are highlighted in the following.
Production of DAMIC-M Skipper CCD:
The CCDs were produced at Teledyne/DALSA in Quebec, Canada, with silicon protected from cosmic-ray activation via underground storage at labs (Boulby, Canfranc, SNOLAB) and transport in a 18-ton steel shielded container. Fabrication at DALSA used an additional shield, and components were sealed and stored to prevent surface contamination. Upon arriving at LSM, CCD silicon had an effective exposure of 80 days, meeting DAMIC-M’s target. The logistical complexity makes this achievement notable.
CCD Module Packaging and Testing:
CCDs were assembled into modules by gluing four CCDs and a low-radioactivity flex cable onto a silicon pitch adapter, then connecting electrically in a cleanroom equipped for semiconductor handling. Special low-radioactivity flex cables were developed for DAMIC-M. Cryogenic testing setups qualified devices, with strict protocols to guard against ESD, radon, and cosmic rays. Of 188 CCDs tested, 112 were used for 28 modules; most modules performed well, except two with major defects. DAMIC-M has achieved the largest production of Skipper CCDs to date.
Detector Cryostat and Shielding:
CCDs are arranged in an array within a vacuum cryostat, surrounded by IR shields and electroformed copper parts with minimal cosmogenic exposure. An external shield consists of nested layers: 5 cm of ancient lead (from a sunken Spanish galleon), 15 cm of low-background lead, and 30 cm of high-density polyethylene. A custom electronics vacuum feedthrough box completes the cryostat.
Electronics:
Custom electronics to operate the skipper CCDs was designed and produced, including a front-end board, to amplify the CCD signal, and a CCD controller, which provides the voltage levels required to move the charge across the CCD and to perform the charge readout. The electronics chain fulfilled the stringent noise specifications, due to the extremely small signals (a charge of one electron generates a signal of ~1 V.)
Low Background Chamber:
The Low Background Chamber (LBC), a DAMIC-M prototype housing up to two CCD modules, began operation at LSM in 2022. Using ancient lead and polyethylene shielding with low-background materials enabled validation of DAMIC-M components under low background levels. The LBC confirmed CCD dark current sufficiency and supported several high-profile scientific publications on low-mass DM searches.
Major scientific results:
We achieved the lowest energy threshold (23 eV) for Compton scattering in silicon, providing crucial calibration for DAMIC-M. Our results show that the Relativistic Impulse Approximation – the standard theory for this process -fails at low energies, requiring improved calculations. This is important for DAMIC-M, as Compton scattering is a major radiogenic background.
We introduced a novel method to search for MeV dark matter via daily modulation signals, the first in this detection channel.
We probed benchmark hidden-sector dark matter models, excluding several candidates for freeze-out and freeze-in scenarios. DAMIC-M is the first experiment with enough sensitivity to probe these scenarios in the MeV mass range, setting world-leading constraints, almost three order of magnitudes better than the state-of-the-art at the time of the ERC proposal.
Dissemination:
DAMIC-M progress and scientific results have been reported in several journal publications and presented at major conferences in the field. DAMIC-M was featured in an article by Le Monde, “Sous une montagne de Savoie, la chasse aux particules de « matière noire », ce monde parallèle qui structure l’Univers”, which includes photographs of the experimental apparatus, and quotes from Privitera and Letessier-Selvon.
DAMIC-M is also prominently featured in the book "Marcel, Lulu et la matière noire", which tells the journey of Marcel and Lulu, a proton and an electron, born with the Big Bang, till being an atom in the eyes of a young researcher, Clara, who is searching for dark matter.
