Search for light dark matter and exploration of the hidden sector with the DAMIC at SNOLAB and DAMIC-M charge-coupled devices
Bibliographic record
Abstract
The existence of electromagnetically inert non-baryonic matter in the universe is supported by a plethora of astrophysical and cosmological observations. Dark matter is expected to account for more than 80% of the mass of the universe. A vast bestiary of particle candidates have been theorized, with the Weakly Interacting Massive Particle (WIMP) paradigm dominating the landscape thanks to its desirable features. Experimental efforts of the last decades have been unsuccessful in detecting WIMPs with weak-scale masses (10-10^4 GeV/c2), thus motivating the search for lighter dark matter. The DAMIC (DArk Matter In CCDs) experiments aim for direct detection of light WIMPs and hidden sector candidates by means of thick silicon Charge-Coupled Devices (CCDs). DAMIC at SNOLAB ~40 g detector sits beneath a 2070 m rock overburden in the Vale Creighton Mine in Canada. Its CCDs are characterized by electron-order readout noise, minimal leakage current (~1E-4 e-/pixel/day) and exquisite spatial resolution (~15 µm). The DAMIC-M kg-scale detector will be hosted in the cleanroom facilities of the Laboratoire Souterrain de Modane (LSM), 1700 m below the Fréjus peak, in France. Its CCDs additionally feature skipper readout amplifiers, which enable sub-electron resolution by means of repeated non-destructive charge measurements. DAMIC-M background goal is 0.1 dru (0.1 events per keV-kg-day), which represents a two orders of magnitude leap relative to SNOLAB apparatus. This thesis work delves into two major themes: the construction of the first comprehensive CCD background model in the context of DAMIC at SNOLAB, and the research and development efforts towards DAMIC-M science goals, particularly with the deployment of its prototype detector, the Low Background Chamber (LBC). The DAMIC at SNOLAB background model is constructed by performing GEANT4 simulations of radioactive contaminants in a virtual detector geometry. Activities are constrained by means of different assay methods. Notably, the spatial coincidence analysis technique unique to Charge-Coupled Devices is leveraged to quantify notorious primordial and cosmogenic isotopes distributed over CCD surface and bulk. Some of the measurements conducted in this fashion vastly outperform more common assay methods. The background model is used to search for light WIMPs in a 11 kg-day exposure dataset. Despite a conspicuous, statistically-significant excess of events below 200 eV, this analysis places the strongest exclusion limit on the WIMP-nucleon spin-independent scattering cross section with a silicon target detector for masses < 9 GeV/c2. DAMIC-M is set to achieve important technological milestones on the way to its science goals. The deployment of skipper CCDs with custom electronics will lower detection thresholds down to ~10 eV, simultaneously enabling higher-precision detector characterization. Cryogenic test chambers are set up across institutions to conduct systematic CCD testing and design a selection process in view of DAMIC-M CCD production. A protocol is defined to establish detector grade and characterize detector performance. The test chamber constructed at LPNHE is additionally used to commission instrumentation for the LBC prototype experiment at LSM. The Low Background Chamber is commissioned for operations in late 2021. High electronic noise (~10 e-) and leakage current (~1E-3 e-/pixel/day) are measured with respect to SNOLAB detectors, highlighting two potential setbacks for DAMIC-M. Despite this, the first science dataset acquired with both LBC skipper CCDs (~20 g) is used to set world-class exclusion limits on the dark matter-electron scattering cross section.
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How this classification was reachedexpand
Full frame machine prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. The Gemma side is a direct model label for every work in the frame, read from the title-only record. The Codex side is a classifier learned from the 10,348 direct Codex labels and calibrated to design-weighted sample rates; fields without enough sample support carry no Codex call. Candidate is the union of the two sides; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels.
Distilled classifier scores by category (both heads)
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.002 | 0.001 |
| Meta-epidemiology (narrow) | 0.001 | 0.000 |
| Meta-epidemiology (broad) | 0.001 | 0.000 |
| Bibliometrics | 0.002 | 0.001 |
| Science and technology studies | 0.001 | 0.001 |
| Scholarly communication | 0.002 | 0.001 |
| Open science | 0.001 | 0.002 |
| Research integrity | 0.001 | 0.001 |
| Insufficient payload (model declined to judge) | 0.005 | 0.002 |
Machine scores (provisional)
The two teacher heads of the student model, read on this work. A score orders the frame for review; it never asserts a category, and the validation status ships verbatim with every row.
Baseline scores from an immature model (maturity gate not passed, 7 training rounds). Scores rank; they never assert a category.
score_only:v0-immature-baseline · verbatim from the scoring run: score_only means the number may rank works, and no category label ships from itClassification
machine, unvalidatedMachine predicted; a candidate call from one source (direct Gemma or distilled Codex), not a consensus.
How this classification was reached, model by model and score by score, is at the end of the page under "How this classification was reached".