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DAMIC-M Dark Matter Limits

Updated 24 September 2025
  • DAMIC-M is a next-generation direct detection experiment using thick, fully depleted silicon CCDs with skipper readout to search for low-mass dark matter.
  • It achieves sub-electron noise and energy thresholds as low as 1–2 electrons by performing multiple non-destructive reads, enabling unprecedented background suppression.
  • The limits set by DAMIC-M significantly constrain both thermal relic and hidden sector dark matter models, reshaping the landscape for sub-GeV dark matter research.

DAMIC-M is a next-generation direct detection experiment utilizing thick, fully depleted silicon charge-coupled devices (CCDs) with skipper readout technology to search for low-mass (<10 GeV/c²) dark matter (DM) at the Laboratoire Souterrain de Modane (LSM), France. Leveraging single-electron sensitivity and ultra-low backgrounds, DAMIC-M has achieved and continues to set world-leading constraints on a diverse set of hidden sector and standard thermal DM candidates. The limits established by DAMIC-M fundamentally shape the landscape of sub-GeV dark matter model building.

1. Experimental Approach: Skipper CCDs, Thresholds, and Backgrounds

DAMIC-M’s core is an array of silicon skipper CCDs, each with 15 μm × 15 μm pixels, thickness up to 670 μm, and high-resistivity substrate to ensure full depletion under substrate bias. The development and implementation of the skipper amplifier is critical: by performing multiple non-destructive reads (N₍skip₎ ≈ 500–650), the charge resolution per pixel is reduced as:

σ=σ1Nskip\sigma = \frac{\sigma_1}{\sqrt{N_{\rm skip}}}

where σ₁ is the RMS single-sample readout noise (~7e⁻ for commercial controllers; ≤3e⁻ with dedicated electronics). This achieves sub-electron noise (typically <0.2e⁻) and energy thresholds as low as 1–2 electrons (~3.6–7 eV), a regime inaccessible to conventional CCDs (Lee et al., 2020, Arnquist et al., 2022, Arnquist et al., 25 Jul 2024).

The LSM site offers suppression of cosmogenic backgrounds and allows deployment of massive passive shields (ancient/Pb, electro-formed copper, HDPE). The prototype Low Background Chamber (LBC) has demonstrated <10 dru (events/keV/kg/day) after installation of improved materials; full-scale DAMIC-M aims for <1 dru (Arnquist et al., 25 Jul 2024, Smida, 30 Sep 2024).

2. Limit-Setting Methodology and Observational Strategy

DAMIC-M searches for ionization signals induced by DM–electron and DM–nucleon scattering in the silicon bulk. Silicon’s indirect bandgap (1.1 eV) allows sensitivity to both nuclear and electronic recoils. For DM–electron searches, the key observable is the number of electrons in spatially-vetted pixel clusters; thermal diffusion and 3D charge reconstruction aid in further background discrimination (Settimo, 2018, Castello-Mor et al., 2020).

Signal and background modeling rely on detailed statistical analyses:

  • Pixel value spectra are fitted using models that convolve Poisson (dark current and leakage) statistics with signal templates (from DM–e⁻ theory and crystal form factors).
  • Joint binned-likelihood analyses are employed across data sets and amplifier channels (Arnquist et al., 2023, Collaboration et al., 18 Mar 2025).
  • Event selection incorporates spatial and temporal vetos, pattern recognition (for charge-sharing due to diffusion), and event cluster topologies.
  • Daily modulation studies search for the time-dependent signature of Earth-shielded MeV DM (Arnquist et al., 2023), increasing robustness and improving sensitivity by ~2 orders of magnitude in some regions.

The detection threshold is typically at the level of 1–2 electrons (≈3.6–7 eV), with conversions for Si: E=electrons×3.6 eVE={\rm electrons}\times 3.6~{\rm eV}.

3. DAMIC-M Constraints on Dark Matter: Key Numerical Results

The DAMIC-M prototype (LBC) has delivered significant exposure improvements (up to ~1.3 kg·days) and a factor of 50 reduction in single-e⁻ rates compared to earlier runs (Collaboration et al., 18 Mar 2025). With these advances, DAMIC-M has established:

  • No statistically significant excess of multi-electron cluster candidates above background expectations. For example:
  • 90% C.L. exclusion limits set on DM–e⁻ cross sections:
  • For electron-coupled dark photon models, DAMIC-M sets world-leading limits on the kinetic mixing ε for hidden photon masses between 1.2–30 eV (Aguilar-Arevalo et al., 2019).
  • For SI WIMP–nucleon scattering, DAMIC sets the strongest silicon-target exclusion for 1 < mₓ < 9 GeV/c² (Traina, 2021).

Exclusion regions (see Table 1 for selected results):

Probe Energy Threshold Mass Range Probed Typical Limit/Result
DM–e⁻ (ultralight mediator) 1–2 e⁻ (~5 eV) 0.53–1000 MeV/c² Exclude mₓ ≳ 1.6 MeV for σ̄ₑ ~ 10⁻³⁸–10⁻³⁶ cm²
DM–e⁻ (heavy mediator) 1–2 e⁻ 1.5–15.1 MeV/c² Exclude mₓ ≳ 1.5 MeV at σ̄ₑ ~ 10⁻³⁷–10⁻³⁶ cm²
Daily modulation 1 e⁻ 0.53–2.7 MeV/c² Improves exclusion by ~2 orders of magnitude (Arnquist et al., 2023)
WIMP–nucleon SI ≈50 eVₑₑ 1–9 GeV/c² Strongest silicon-based σₙ exclusion (Traina, 2021)

4. Theoretical Implications: Thermal and Hidden Sector Models

The DAMIC-M limits robustly constrain both canonical thermal relic models and a broad array of hidden sector scenarios. In particular:

  • Scalar DM with dark photon mediator: DAMIC-M excludes regions where the mediator-to-DM mass ratio R=mA/mχ2.8\mathcal{R}=m_{A'}/m_\chi \gtrsim 2.8 for mχ20m_\chi\sim20–$200$ MeV, which eliminates large portions of the parameter space where freeze-out would provide the correct relic abundance (Cheek et al., 21 Jul 2025, Collaboration et al., 18 Mar 2025, Smida, 30 Sep 2024).
  • Asymmetric (Dirac) fermion DM: Windows allowed by previous searches are now closed except for small regions at mχ15m_\chi\sim15–$20$ MeV (Cheek et al., 21 Jul 2025).
  • Freeze-in and freeze-out scenarios (hidden sector DM): Large windows for complex scalar or fermionic dark matter produced via either mechanism (mediated by an ultra-light or heavy vector) are now excluded for 3MeV/c2mχ490MeV/c23\,\text{MeV/c}^2\,\lesssim m_\chi \lesssim\,490\,\text{MeV/c}^2 (freeze-in, ultra-light mediator) and 2.9MeV/c2mχ21.5MeV/c22.9\,\text{MeV/c}^2\,\lesssim m_\chi \lesssim\,21.5\,\text{MeV/c}^2 (freeze-out, heavy mediator) assuming these particles are the dominant relic (Collaboration et al., 18 Mar 2025, Cheek et al., 21 Jul 2025).
  • Self-interacting DM: Family-universal U(1)_X models, compatible with limits, yield strong DM self-interactions V(r)=±gd24πreMXrV(r) = \pm \frac{g_d^2}{4\pi r} e^{-M_X r}, relevant for small-scale structure (Borah et al., 19 Sep 2025).

5. DAMIC-M Design Progress and Low Background Achievement

Developments detailed in (Arnquist et al., 25 Jul 2024, Smida, 30 Sep 2024) mark technical advances:

  • Demonstration of background rates below ~7 dru after deployment of prototype modules in the LBC.
  • Careful selection of materials (ancient lead, electro-formed copper), operation at ~130 K, and advanced readout electronics have successfully suppressed non-signal backgrounds.
  • With a projected full exposure of ≈1 kg·year (from ~700 g silicon, ~200 CCDs) and continued improvements in CCD packaging and shielding, DAMIC-M is positioned for leading sensitivity to both DM–electron and DM–nucleon interactions over an expanded mass range.
  • Ongoing tests validate stable, low dark current performance and high-efficiency veto of correlated and instrumental backgrounds.

6. Comparative Landscape and Complementary Constraints

The DAMIC-M results are complementary to, and in some regimes more stringent than, existing direct searches such as PandaX-4T (S2-only), SENSEI, and SuperCDMS (Cheek et al., 21 Jul 2025). PandaX-4T supersedes DAMIC-M’s bounds in a select regime (20–200 MeV for heavy mediators), while DAMIC-M’s lower threshold dominates for light mediators and in the ultra-light DM mass region.

The integration of DAMIC-M data with CMB, beam-dump, and accelerator limits further restricts viable model parameter space, particularly for models with gauge boson mediators (e.g., Lμ–Lτ scenarios, family-universal U(1)_X). For U(1)₍Lμ–τ₎, DAMIC-M’s suppressed DM–e coupling favors a narrow resonance region, to be further tested by muon g–2 and fixed target/beam experiments (Borah et al., 19 Sep 2025).

7. Outlook and Future Prospects

DAMIC-M’s technology and analysis approach lay the foundation for next-generation low-mass dark matter explorations. The experiment’s planned scale-out to ~1 kg target mass and the already demonstrated low-threshold performance will enhance sensitivity to currently marginal scenarios, particularly those involving complex mediator structure or non-standard production mechanisms.

Further anticipated directions include:

  • Extended exposures to refine limits and probe signal time-domain features (e.g., annual modulation).
  • Adoption of advanced theoretical models for DM–electron scattering rate calculations (QEdark, QCDark, DarkELF, EXCEED-DM) to further reduce uncertainties in exclusion boundary interpretation.
  • Introduction of more massive and radiopure detector arrays, achieving exposure levels necessary to probe WIMP–nucleon cross sections below the so-called neutrino floor in the silicon mass range.

DAMIC-M’s systematic campaign to lower thresholds, backgrounds, and instrumental noise continues to advance the dark matter frontier, delivering constraints that are central to ongoing model differentiation in particle and astroparticle physics.

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