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1. The DAMIC-M Low Background Chamber

   https://doi.org/10.1088/1748-0221/19/11/T11010  

   Arnquist, I; Avalos, N; Bailly, P; Baxter, D; Bertou, X; Bogdan, M; Bourgeois, C; Brandt, J; Cadiou, A; Castelló-Mor, N; et al (November 2024, Journal of Instrumentation)

   Abstract The DArk Matter In CCDs at Modane (DAMIC-M) experiment is designed to search for light dark matter (m_χ< 10 GeV/c²) at the Laboratoire Souterrain de Modane (LSM) in France. DAMIC-M will use skipper charge-coupled devices (CCDs) as a kg-scale active detector target. Its single-electron resolution will enable eV-scale energy thresholds and thus world-leading sensitivity to a range of hidden sector dark matter candidates. A DAMIC-M prototype, the Low Background Chamber (LBC), has been taking data at LSM since 2022. The LBC provides a low-background environment, which has been used to characterize skipper CCDs, study dark current, and measure radiopurity of materials planned for DAMIC-M. It also allows testing of various subsystems like readout electronics, data acquisition software, and slow control. This paper describes the technical design and performance of the LBC. 

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2. Probing Benchmark Models of Hidden-Sector Dark Matter with DAMIC-M

   https://doi.org/10.1103/2tcc-bqck  

   Aggarwal, K; Arnquist, I; Avalos, N; Bertou, X; Castelló-Mor, N; Chavarria, A E; Cuevas-Zepeda, J; Dastgheibi-Fard, A; De_Dominicis, C; Deligny, O; et al (August 2025, Physical Review Letters)

   We report on a search for sub-GeV dark matter (DM) particles interacting with electrons using the DAMIC-M prototype detector at the Modane Underground Laboratory. The data feature a significantly lower detector single $e^{-}$rate (factor 50) compared to our previous search, while also accumulating a 10 times larger exposure of $\sim 1.3\mathrm{kg}\text{−}\mathrm{day}$. DM interactions in the skipper charge-coupled devices (CCDs) are searched for as groups of two or three adjacent pixels with a total charge between 2 and $4e^{-}$. We find 144 candidates of $2e^{-}$and 1 candidate of $4e^{-}$, where 141.5 and 0.071, respectively, are expected from background. With no evidence of a DM signal, we place stringent constraints on DM particles with masses between 1 and $1000\mathrm{MeV}/c^2$interacting with electrons through an ultralight or heavy mediator. For large ranges of DM masses below $1\mathrm{GeV}/c^2$, we exclude theoretically motivated benchmark scenarios where hidden-sector particles are produced as a major component of DM in the Universe through the freeze-in or freeze-out mechanisms. 

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3. Even lighter particle dark matter

   https://doi.org/10.21468/SciPostPhysProc.12.001  

   Chavarria, Alvaro E. (July 2023, SciPost Physics Proceedings)

   We report on recent progress in the search for dark matter particleswith masses from 1 Mev c ^{-2} − 2 to 1 Gev c ^{-2} − 2 .Several dark matter candidates in this mass range are expected togenerate measurable electronic-recoil signals in direct-detectionexperiments. We focus on dark matter particles scattering with electronsin semiconductor detectors since they have fundamentally the highestsensitivity due to their low ionization threshold. Charge-coupled device(CCD) silicon detectors are the leading technology, with significantprogress expected in the coming years. We present the status of the CCDprogram and briefly report on other efforts. 

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4. EXCESS workshop: Descriptions of rising low-energy spectra

   https://doi.org/10.21468/SciPostPhysProc.9.001  

   Adari, Prakruth; Aguilar-Arevalo, Alexis A.; Amidei, Dante; Angloher, G.; Armengaud, Eric; Augier, C.; Balogh, Levente; Banik, S.; Baxter, David; Beaufort, C.; et al (January 2022, SciPost Physics Proceedings)

   Many low-threshold experiments observe sharply rising event rates of yet unknown origins below a few hundred eV, and larger than expected from known backgrounds. Due to the significant impact of this excess on the dark matter or neutrino sensitivity of these experiments, a collective effort has been started to share the knowledge about the individual observations. For this, the EXCESS Workshop was initiated. In its first iteration in June 2021, ten rare event search collaborations contributed to this initiative via talks and discussions. The contributing collaborations were CONNIE, CRESST, DAMIC, EDELWEISS, MINER, NEWS-G, NUCLEUS, RICOCHET, SENSEI and SuperCDMS. They presented data about their observed energy spectra and known backgrounds together with details about the respective measurements. In this paper, we summarize the presented information and give a comprehensive overview of the similarities and differences between the distinct measurements. The provided data is furthermore publicly available on the workshop's data repository together with a plotting tool for visualization. 

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5. Spectroscopy and crystallography define carotenoid oxygenases as a new subclass of mononuclear non-heme FeII enzymes

   https://doi.org/10.1016/j.jbc.2025.108444  

   DeWeese, Dory E; Everett, Michael P; Babicz, Jeffrey T; Daruwalla, Anahita; Solomon, Edward I; Kiser, Philip D (March 2025, Journal of Biological Chemistry)

   NA (Ed.)

   Carotenoid cleavage dioxygenases (CCDs) are non-heme FeII enzymes that catalyze the oxidative cleavage of alkene bonds in carotenoids, stilbenoids, and related compounds. How these enzymes control the reaction of O2 with their alkene substrates is unclear. Here, we apply spectroscopy in conjunction with X-ray crystallography to define the iron coordination geometry of a model CCD, CAO1, in its resting state and following substrate binding and coordination sphere substitutions. Resting CAO1 exhibits a five-coordinate (5C), square pyramidal FeII center that undergoes steric distortion towards a trigonal bipyramidal geometry in the presence of piceatannol. Titrations with the O2-analog, nitric oxide (NO), show a >100-fold increase in iron-NO affinity upon substrate binding, defining a crucial role for the substrate in activating the FeII site for O2 reactivity. The importance of the 5C FeII structure for reactivity was probed through mutagenesis of the second-sphere Thr151 residue of CAO1, which occludes ligand binding at the sixth coordination position. A T151G substitution resulted in the conversion of the iron center to a six-coordinate (6C) state and a 135-fold reduction in apparent catalytic efficiency towards piceatannol compared to the wild-type enzyme. Substrate complexation resulted in partial 6C to 5C conversion, indicating solvent dissociation from the iron center. Additional substitutions at this site demonstrated a general functional importance of the occluding residue within the CCD superfamily. Taken together, these data suggest an ordered mechanism of CCD catalysis occurring via substrate-promoted solvent replacement by O2. CCDs thus represent a new class of mononuclear non-heme FeII enzymes. 

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