---
title: 'DAMIC-M: Silicon CCD Dark Matter Detector'
url: https://www.emergentmind.com/topics/damic-m
type: topic
---

# DAMIC-M: Silicon CCD Dark Matter Detector

DAMIC-M, usually expanded as **DArk Matter In CCDs at Modane**, is a silicon CCD-based direct-detection experiment developed to search for very low-energy interactions from low-mass dark matter and related hidden-sector scenarios at the Laboratoire Souterrain de Modane in France. It is the next-generation continuation of the DAMIC program at SNOLAB, retaining the use of fully depleted, high-resistivity silicon as both target and imaging detector while replacing conventional CCD readout with skipper readout that provides single-electron or sub-electron charge resolution. Across its design, prototype, and early-physics literature, DAMIC-M is defined by eV-scale thresholds, very low dark current, three-dimensional event reconstruction from charge diffusion, and a staged move from a prototype Low Background Chamber to a larger underground detector optimized for sub-GeV dark-matter searches through both electronic and nuclear recoils [1805.10001][2001.01209][2210.12070][2409.20290].

## 1. Lineage within the DAMIC program

DAMIC-M emerged from the CCD-based dark-matter program established by DAMIC at SNOLAB. In that predecessor configuration, the detector used seven fully depleted CCDs with a total active mass of **40 g**; each CCD was a **16-Mpixel** device with pixel size **$(15\times15)\,\mu\mathrm{m}^{2}$** and thickness **675 $\mu$m**, housed in a copper box cooled to **140 K** inside vacuum and shielded by **18 cm of lead**, with the innermost **2 inches** made of ancient lead, plus **42 cm of polyethylene** for neutron suppression [1805.10001]. The SNOLAB apparatus exploited the low nuclear mass of silicon for sensitivity to WIMPs in the range **1–10 GeV/$c^{2}$**, while the silicon band gap provided sensitivity to dark-matter–electron interactions depositing as little as **1.1 eV** in the target [1805.10001].

The early DAMIC literature had already established the central experimental logic that later defined DAMIC-M: thick, fully depleted CCDs can deliver very low ionization thresholds, low noise, and a scalable silicon target for dark matter below **10 GeV** [1310.6688]. Subsequent DAMIC analyses at SNOLAB reported leakage current as low as **$10^{-3}$ e$^-$/pix/day** at **140 K**, Gaussian pixel noise of about **$\sim 1.6$ electrons**, and a likelihood-based image scan with discriminant
\[
\Delta LL = \mathcal{L}_n - \mathcal{L}_G
\]
to separate noise from signal-like clusters [1805.10001]. In that context, preliminary analysis suggested an energy threshold of **50 eV$_{ee}$** with an expected leakage of only **0.01 noise events** over the full data set, and background levels of **2 DRU** for the CCD sandwiched between ancient-lead blocks and **5 DRU** for the others in the **0.5–14.5 keV** range [1805.10001].

DAMIC-M was formulated as the next step beyond that 40 g SNOLAB array. The 2018 DAMIC paper described DAMIC-M as a Modane installation with a total mass of **1 kg**, new CCDs with **36 Mpixels** each, **1 mm** thickness, and about **20 g** mass per CCD, combined with skipper readout to target a **2-electron ionization threshold** and background levels reduced to **fractions of a DRU** [1805.10001]. Later overview papers reiterated that the purpose of the upgrade was not merely increased target mass but the combination of larger exposure, sub-electron charge resolution, and lower radioactive and instrumental backgrounds [2003.09497][2001.01476].

## 2. Detector principle and skipper-CCD technology

The detector principle is inherited from DAMIC: the bulk silicon of a fully depleted scientific CCD acts simultaneously as the interaction target and the sensor. Ionization charge created by a particle interaction drifts through the silicon bulk to the pixel plane; during drift, the charge diffuses laterally, so the final pixel cluster encodes depth information through its spatial extent [2001.01209]. This depth sensitivity is one of the defining features of the DAMIC/DAMIC-M approach, because it enables three-dimensional reconstruction and rejection of surface backgrounds [2001.01476].

The CCDs used in DAMIC-M are described as high-resistivity n-type silicon devices with **15 $\mu$m $\times$ 15 $\mu$m** pixels and thicknesses around **670–675 $\mu$m**, fully depleted at substrate biases of at least **40 V** or, in one prototype configuration, **70 V** [2302.02372][2409.20290]. DAMIC-M’s key innovation is the **skipper amplifier**, which permits **multiple non-destructive charge measurements** of the same pixel. In the design literature, the corresponding noise reduction is described by the familiar scaling
\[
\sigma_{N_{\rm skip}} = \frac{\sigma_1}{\sqrt{N_{\rm skip}}}
\]
or equivalently as noise decreasing approximately as the inverse square root of the number of repeated measurements [2210.12070][2407.17872].

This readout concept is what places DAMIC-M in the single-electron regime. The 2020 instrumentation paper reported prototype skipper performance with readout noise **\SI{0.068}{\electron}** and a demonstrated sub-electron value of
\[
(7.22 \pm 0.05)\times 10^{-2}\ e^- ,
\]
stating that this performance, combined with low leakage current, would allow processes with collision energies as low as **1 eV** to be observed [2001.01209]. Another 2020 overview cited **0.07 e⁻** readout noise demonstrated with **4000 samples per pixel**, and also gave the ionization calibration relation **`3.8 eV_ee = 1e^-`** [2001.01476]. In the first underground DAMIC-M runs, the collaboration used **650 skipper samples per pixel**, reaching a charge resolution of about **0.2 $e^-$** [2302.02372]. In the later pattern-based prototype search, the quoted charge resolution was
\[
\sigma_{ch} \sim 0.16\,e^- ,
\]
which is the regime needed to distinguish 1-, 2-, 3-, and 4-electron deposits [2503.14617].

The choice of silicon is central to the physics program. The experiment is explicitly designed to search for dark matter too light to produce conventional detectable nuclear recoils in many other detectors, making **dark matter–electron scattering** a primary channel [2503.14617]. At the same time, the DAMIC literature consistently emphasizes that the same detector architecture remains sensitive to low-mass WIMPs through nuclear recoils, to hidden-photon absorption, and to other low-energy processes in silicon [2001.01209][2001.01476].

## 3. Experimental realizations at Modane

DAMIC-M is operated at the **Laboratoire Souterrain de Modane (LSM)**, beneath roughly **4800 m.w.e.** of overburden. The Low Background Chamber paper describes LSM as about **1700 m below the Fréjus Peak**, with cosmic-ray muons suppressed to **5.4 $\mu$/m$^2$/day**, and notes that the DAMIC-M infrastructure includes an **ISO 5 cleanroom** and **ISO 6 gowning room** built for underground handling of CCDs and electronics [2407.17872]. Environmental measurements reported there include a median radon concentration of **\(18.4 \pm 8.5\) Bq/m\(^3\)**, with **99%** of values below **42 Bq/m\(^3\)**, as well as gamma and neutron flux measurements relevant to low-background operation [2407.17872].

The first underground DAMIC-M prototype was the **Low Background Chamber (LBC)**. In its original configuration, the LBC used **two 6k $\times$ 4k CCDs** with **669 $\mu$m** thickness and active mass about **8.9 g** per CCD setup [2407.17872]. The first DAMIC-M dark-matter search, however, is described in the collaboration’s 2023 results paper as using **two large, thick skipper CCDs** in the LBC, each about **9 g** and **670 μm** thick, for a total integrated exposure of **85.23 g days** split between SR1 and SR2 [2302.02372]. The daily-modulation paper based on the same early period specifies **63 days of uninterrupted data** starting on **June 8, 2022**, with a final clean exposure of **39.97 g-days** over **8779 images** [2307.07251].

The LBC later evolved toward the final DAMIC-M module format. A second configuration installed **two CCD modules**, each with **four 6k $\times$ 1.5k CCDs** mounted on silicon pitch adapters; the LBC paper states that these modules are close to what will be used in the final detector [2407.17872]. The 2025 benchmark-model search used this module-style prototype geometry: **two CCD modules**, **eight CCDs total**, and **six** CCDs retained for analysis after excluding two problematic devices. Each of those CCDs had
\[
6144 \times 1536 \text{ pixels},
\]
pixel size **\(15\times 15\,\mu\mathrm{m}^2\)**, thickness **\(670\,\mu\mathrm{m}\)**, and mass **\(\sim 3.3\) g** [2503.14617].

Published descriptions of the full detector evolved across stages. Early design documents described a **kg-scale array of 50 CCDs** with a total active mass of about **1 kg**, using **1 mm-thick, 36 Mpixel** sensors of about **20 g** each [1805.10001][2001.01476]. A 2020 instrumentation paper described a final detector of **50 large-area skipper CCDs** with **more than 36 million pixels** in each CCD [2001.01209]. By 2022 and 2024, status papers described a detector with about **200** or **208** large-format skipper CCDs of roughly **3.3–3.5 g** each, totaling about **700 g**, while abstracts still referred to “about **1 kg**” of silicon target mass [2210.12070][2409.20290]. The first production paper then reported the fabrication of **28 CCD modules**, each containing **four 9-megapixel skipper CCDs**, with **26 modules**—about **350 g active mass**—selected for the first underground deployment planned for **early 2026** [2509.06943].

## 4. Background control, imaging, and detector characterization

Background suppression in DAMIC-M combines passive shielding, material radiopurity, optical and thermal control, and event-topology reconstruction. The LBC design uses a cold copper housing, an inner shield of at least **6 cm of lead** around the CCD box, the innermost **2 cm** made of **ancient Roman lead**, and an external shield of **15–20 cm lead and HDPE**, depending on location [2407.17872]. In the prototype program, external shielding reduced the event rate by a factor of **50**; the background between **1 and 6 keV** excluding silicon K lines decreased from **\(12.5\pm2.8\) dru** to **\(6.7\pm1.1\) dru**, closely matching the Geant4 prediction of **5.46 dru** for the mitigation step that was applied [2407.17872].

Material assays and cosmogenic-activation control are treated as central engineering constraints. The LBC paper reports assay values in **mBq/kg** for CCD flex, OFHC copper, electro-formed copper, and other components, and identifies the replacement of OFHC copper lids by electro-formed copper as a major background improvement [2407.17872]. The module-production paper makes the same point at the scale of detector fabrication: the design budget required an overall background below
\[
\lesssim 1~\text{event}\cdot \text{keV}^{-1}\text{kg}^{-1}\text{day}^{-1},
\]
with each major source contributing at most about
\[
0.1~\text{event}\cdot \text{keV}^{-1}\text{kg}^{-1}\text{day}^{-1}
\]
to the region of interest [2509.06943]. That paper also quantified residual contamination from production, including a cosmogenic tritium increase of
\[
A_{\text{trit}} = 0.96 \pm 0.20~\upmu\text{Bq/kg},
\]
front-surface \(^{210}\)Pb of
\[
A_{\text{lead}} = 0.39 \pm 0.31~\text{nBq/cm}^2,
\]
and particulate activities from wire bonding that were reported as acceptable relative to the DAMIC-M budget [2509.06943].

At the analysis level, DAMIC-M relies on the fact that a bulk interaction in a fully depleted CCD generally diffuses into a small cluster rather than an isolated pixel. The 2025 prototype search therefore abandoned a purely single-pixel strategy for its main analysis and instead looked for **two or three consecutive pixels in the same row**, with total charge between **2 and 4 electrons**. The searched patterns were
\[
\{11\},\ \{21\},\ \{111\},\ \{31\},\ \{22\},\ \{211\},
\]
with pattern-identification variables \(p_{mn}\) and \(p_{mnl}\), and thresholds \(p_{mn}<4\) and \(p_{mnl}<5.5\) that yielded about **90% pattern-classification efficiency** [2503.14617]. The same paper imposed further conditions—no additional charge above \(1e^-\) in adjacent rows, no corresponding charge in the other CCDs of the same module, and no extra \(\ge 2e^-\) pixel in candidate columns—to reduce random coincidences and correlated noise backgrounds [2503.14617].

Temporal stability and non-ionizing signatures have also been studied as detector observables. A 2025 daily-modulation analysis found a correlation between the single-electron rate and the external system temperature, modeled as
\[
r^i = r_0 + \alpha_T T_i ,
\]
and attributed to infrared photons from room-temperature components [2511.13962]. Separately, a 2022 radiation-damage study irradiated a **24-megapixel DAMIC-M CCD** with an **AmBe neutron source** and reported, for the first time, that **individual defects produced by nuclear recoils** can be identified in a DAMIC-M CCD. That paper found that **at least 80%** of nuclear recoils above **\(100~\mathrm{keV}_{ee}\)** were spatially correlated with a defect appearing after irradiation, suggesting a possible route to nuclear/electron recoil discrimination in some energy ranges [2210.00469]. This suggests an additional analysis channel beyond ionization topology alone.

## 5. Searches and published physics results

The first underground DAMIC-M search for dark matter interacting with electrons used an integrated exposure of
\[
85.23 \, \mathrm{g\,days},
\]
split into **45.26 g-days** in SR1 and **39.97 g-days** in SR2 [2302.02372]. The analysis searched pixel charges up to **7e$^-$**, calibrated the charge scale using the **0e, 1e, 2e** peaks, and performed a joint binned likelihood fit over four charge distributions, one for each amplifier in each run [2302.02372]. No preference for a dark-matter signal was found, and the collaboration set **90% C.L.** limits on dark-matter–electron scattering over the mass range **0.53 to 1000 MeV/$c^2$**, excluding unexplored parameter space in **[1.6,1000] MeV/$c^2$** for ultralight mediators and **[1.5,15.1] MeV/$c^2$** for heavy mediators [2302.02372].

A distinct line of analysis used time dependence rather than total rate. The 2023 daily-modulation study searched the SR2 sample for a sidereal modulation of the **1$e^-$** event rate, motivated by the possibility that sufficiently strongly interacting dark matter may scatter in Earth’s bulk before detection [2307.07251]. Its model-independent fit used
\[
F(t)=B e^{-t/\tau}+C+A\cos\!\left(\frac{2\pi(t-\phi)}{T}\right),
\]
and found **no evidence for modulation at the sidereal period**, \(T=23.93\) h [2307.07251]. Interpreted in a dark-photon-mediated DM–electron scattering model, the same **39.97 g-day** dataset yielded exclusion limits for masses in the range **0.53 to 2.7 MeV/$c^2$**, improving the collaboration’s previous total-rate limit by **about 2 orders of magnitude** and, according to the paper, constituting the **current strongest limit on DM-electron scattering via ultralight mediators around \(m_\chi \sim 1\) MeV/\(c^2\)** [2307.07251].

The 2025 prototype search substantially increased the exposure and lowered the single-electron background rate. Using **84 days** of data between **October 2024 and January 2025**, the collaboration obtained **D1: 0.139 kg-day** and **D2: 1.257 kg-day**, for a total of about **1.3 kg-day**, while reporting a **factor of 50 reduction in the single-electron rate** relative to the earlier DAMIC-M search [2503.14617]. The measured single-electron rate in D2 was
\[
2.4-3.1\times 10^{-4}\ e^-/\text{pixel}/\text{image},
\]
equivalent to roughly **350–460 \(e^-\)/g/day** [2503.14617]. In the blinded D2 sample, the analysis found **144 candidates** for \(\{11\}\), **1 candidate** for \(\{31\}\), and **0 candidates** for \(\{21\}, \{111\}, \{22\}, \{211\}\), compared with expected backgrounds of **141.5** for total \(\{11\}\)-like backgrounds and **0.071** for \(\{31\}\) [2503.14617]. The paper concluded that there was **no evidence for a dark matter signal** and set **90% C.L. upper limits** for masses between **1 and 1000 MeV/$c^2$** [2503.14617].

That null result was then mapped onto benchmark hidden-sector models. For an **ultra-light mediator**, the paper states that DAMIC-M excludes dark matter as the **dominant component of cosmological dark matter via freeze-in** for masses in the range
\[
3.5 \text{ to } 490\ \mathrm{MeV}/c^2.
\]
For the **heavy-mediator** benchmark of **complex scalar dark matter** freezing out in the early Universe, DAMIC-M excludes the scenario for masses between
\[
2.9 \text{ and } 21.5\ \mathrm{MeV}/c^2,
\]
and notes that only a narrow region around **25 MeV/\(c^2\)** remains viable in that benchmark when all relevant constraints are combined [2503.14617].

A later daily-modulation analysis used the **1.257 kg-day** D2 dataset collected with the LBC and searched for periodicity in the single-electron rate over periods from **1 to 48 h** [2511.13962]. After temperature-dependent background subtraction and periodogram analysis, it reported **no significant modulation** and emphasized the detector’s temporal stability [2511.13962]. In a complementary model-dependent analysis of Hidden Sector dark matter with masses in **[0.53,2] MeV/$c^2$**, the paper states that the resulting limits improve over previous DAMIC-M constraints by **up to about two orders of magnitude** below **1.2 MeV/$c^2$**, and are the **strongest published limits for Galactic halo DM in the mass range 0.53–1.22 MeV/$c^2$** [2511.13962].

## 6. Theoretical interpretation and position in sub-GeV dark-matter phenomenology

Recent phenomenology has treated DAMIC-M as a benchmark experiment for sub-GeV direct detection through electron recoils. A 2025 comparative analysis states that the DAMIC-M collaboration had “**recently reported impressive bounds on sub-GeV dark matter**” that “**robustly test both thermal and non-thermal models for the very first time**” [2507.15956]. In that paper, PandaX-4T S2-only data are found to **compete with the DAMIC-M results**, providing the best constraints for scalar and asymmetric thermal dark matter models between **20 and 200 MeV**, while DAMIC-M remains stronger for **light or massless mediators** [2507.15956]. The comparison makes explicit that DAMIC-M occupies the low-threshold, low-mass end of the current direct-detection landscape rather than a merely ancillary role.

The formalism used in DAMIC-M analyses is also standard within semiconductor dark-matter searches. The collaboration’s electron-scattering papers write the differential rate in the schematic form
\[
\frac{\mathrm{d}R}{\mathrm{d}E_e} \propto \bar{\sigma}_e \int \frac{\mathrm{d}q}{q^2} \left[\int \frac{f(\mathbf{v})}{v}\,\mathrm{d^3v}\right] |F_\mathrm{DM}(q)|^2 |F_\mathrm{c}(q,E_e)|^2,
\]
with
\[
F_\mathrm{DM}(q)=\left(\frac{\alpha m_e}{q}\right)^n ,
\]
where \(n=0\) corresponds to a **heavy mediator** and \(n=2\) to an **ultra-light mediator** [2302.02372][2503.14617]. Because DAMIC-M can resolve individual or few-electron deposits, it is especially relevant to models in which the visible signal is concentrated in the lowest ionization multiplicities.

Model-building papers from 2025 and 2026 sharpened this role. One study of light thermal dark matter in the light of DAMIC-M 2025 constraints concluded that the new electron-recoil limits are among the most important tests of **sub-GeV thermal dark matter**, but do **not** eliminate all viable models; instead they leave only narrow, predictive regions in the examples considered, such as a resonant \(U(1)_{L_\mu-L_\tau}\) band with
\[
M_{Z_{\mu\tau}} \gtrsim 30~\text{MeV}
\]
and typically
\[
m_\chi \simeq \frac{M_{Z_{\mu\tau}}}{2}
\]
[2509.16319]. Another 2026 study used a projected DAMIC-M sensitivity to intermediate-mass mediators and argued that, for freeze-in-sized couplings, DAMIC-M is sensitive to dark-photon masses up to about
\[
m_{A'} \lesssim 10 \,\text{keV},
\]
highlighting that the experimentally relevant distinction between light and heavy mediators spans a broad intermediate regime rather than a single crossover scale [2605.11063].

In cosmological applications, DAMIC-M constraints have been recast into statements about production mechanisms and early-Universe history. A 2026 freeze-in analysis states that recent DAMIC-M and PandaX results exclude the **standard freeze-in** production of dark matter for masses in the range
\[
3~\mathrm{MeV} \lesssim m_\chi \lesssim 1~\mathrm{GeV}
\]
in an ultra-light \(U(1)_X\) gauge-boson framework, and further argues that direct-detection limits on \(\overline{\sigma}_{\rm e}\) can translate into lower bounds on the reheating temperature in low-\(T_{\rm RH}\) freeze-in scenarios [2606.12408]. This suggests that DAMIC-M has become relevant not only for detector-scale sensitivity studies but also for testing the cosmological consistency of hidden-sector constructions.

A recurrent misconception is to treat DAMIC-M as simply a larger DAMIC. The published record does not support that reduction. From the earliest design papers onward, the defining changes are the move to skipper readout, the attempt to reach single-electron sensitivity, the redesign of packaging and materials to reduce backgrounds, and the use of imaging information—cluster morphology, diffusion-based depth reconstruction, and, in some studies, time-domain modulation or defect formation—as part of the signal discrimination strategy [1805.10001][2001.01209][2407.17872]. In that sense, DAMIC-M is best understood as the CCD rare-event program’s transition from low-threshold proof of principle to a dedicated sub-GeV dark-matter experiment whose prototype data already constrain benchmark thermal and non-thermal models.

Source: https://www.emergentmind.com/topics/damic-m