We report constraints on sub-GeV dark matter particles interacting with electrons from the first underground operation of DAMIC-M detectors. The search is performed with an integrated exposure of 85.23 g days, and exploits the subelectron charge resolution and low level of dark current of DAMIC-M charge-coupled devices (CCDs). Dark-matter-induced ionization signals above the detector dark current are searched for in CCD pixels with charge up to 7e^{-}. With this dataset we place limits on dark matter particles of mass between 0.53 and 1000 MeV/c^{2}, excluding unexplored regions of parameter space in the mass ranges [1.6,1000] MeV/c^{2} and [1.5,15.1] MeV/c^{2} for ultralight and heavy mediator interactions, respectively. 

/pdf/first-constraints-from-damic-m-on-sub-gev-dark-matter-11kuyx7v.pdf

First Constraints from DAMIC-M on Sub-GeV Dark-Matter Particles Interacting with Electrons

In rocks or artificial geo-materials, radioactive isotopes emitting alpha particles are dispersed according to the mineralogy. At hand specimen scale, the achievement of quantitative chemical mapping of these isotopes takes on a specific importance. Knowledge of the distribution of the uranium and thorium series radionuclides is of prime interest to several disciplines, from the geochemistry of uranium deposits, to the dispersion of uranium mill tailings in the biosphere. The disequilibrium of these disintegration chains is also commonly used for dating. However, some prime importance isotopes, such as 226 Ra, are complicated to localize in geo-materials. Because of its high specific activity, 226 Ra is found in very low concentrations (~ppq), preventing its accurate localization in rock forming minerals. This paper formulates a quantitative answer to the following question: at hand specimen scale, how can alpha emitters in geo-materials be mapped quantitatively? In this study, we tested a new digital autoradiographic method (called the Beaver™) based on a Micro Patterned Gaseous Detector (MPGD) in order to quantitatively map alpha emission at the centimeter scale rock section. Firstly, for two thin sections containing U-bearing minerals at secular equilibrium, we compared the experimental and theoretical alpha count rates, measured by the Beaver™ and calculated from the uranium content, respectively. We found that they are very similar. Secondly, for a set of eight homemade standards made up of a mixture of inactive sand and low-radioactivity mud, we compared the count rates obtained by the Beaver™ and by an alpha spectrometer. The results indicate (i) a linearity between both count rates, and (ii) that the count obtained by the Beaver™ can be estimated from the count obtained by the alpha spectrometry using a factor of 0.82.

Quantitative autoradiography of alpha particle emission in geo-materials using the Beaver™ system

The first performance tests are presented of a carbon-14 (14C) beta-particle digital autoradiography system with an energy-sensitive hybrid silicon pixel detector based on the Timepix readout circuit. Timepix was developed by the Medipix2 Collaboration and it is similar to the photon-counting Medipix2 circuit, except for an added time-based synchronization logic which allows derivation of energy information from the time-over-threshold signal. This feature permits direct energy measurements in each pixel of the detector array. Timepix is bump-bonded to a 300 ?m thick silicon detector with 256 ? 256 pixels of 55 ?m pitch. Since an energetic beta-particle could release its kinetic energy in more than one detector pixel as it slows down in the semiconductor detector, an off-line image analysis procedure was adopted in which the single-particle cluster of hit pixels is recognized; its total energy is calculated and the position of interaction on the detector surface is attributed to the centre of the charge cluster. Measurements reported are detector sensitivity, (4.11 ? 0.03) ? 10?3 cps mm?2 kBq?1 g, background level, (3.59 ? 0.01) ? 10?5 cps mm?2, and minimum detectable activity, 0.0077 Bq. The spatial resolution is 76.9 ?m full-width at half-maximum. These figures are compared with several digital imaging detectors for 14C beta-particle digital autoradiography.

14C autoradiography with an energy-sensitive silicon pixel detector.

Mobility of daughter elements of 238U decay chain during leaching by In Situ Recovery (ISR): New insights from digital autoradiography.

Mapping 238U decay chain equilibrium state in thin sections of geo-materials by digital autoradiography and microprobe analysis

Autoradiography is a widely used technique in pharmacology and biological fields. It is able to localize in 2 dimensions molecules labeled with beta emitters. The gaseous detector incorporating micromesh Parallel Ionization Multiplier (PIM) has already shown its ability to localize precisely electrons from low-energy emitters like 3 H and 14 C with a high resolution or on a large area. We report on a new prototype devoted to precise determination of beta emitters. It could be used to image gamma emitters distribution by using autoradiography of the associated beta particles present on a large number of useful gamma radioelements such as 131 I, 46 Sc, 18 F, etc. By proceeding with a dedicated method, we expect to locate in 2 dimensions the position of gamma emitter with a precision greater than 150 μm. This new prototype could also be used for traditional low-energy beta autoradiography of 3 H, 14 C or 125 I with a spatial resolution better than 50 μm and real-time imaging. First results obtained with this new prototype are presented.

The micro-pattern gas detector PIM: A multi-modality solution for novel investigations in functional imaging

The DAMIC-M (DArk Matter In CCDs at Modane) experiment employs thick, fully depleted silicon charged-coupled devices (CCDs) to search for dark matter particles with a target exposure of 1 kg-year. A novel skipper readout implemented in the CCDs provides single electron resolution through multiple non-destructive measurements of the individual pixel charge, pushing the detection threshold to the eV-scale. DAMIC-M will advance by several orders of magnitude the exploration of the dark matter particle hypothesis, in particular of candidates pertaining to the so-called “hidden sector.” A prototype, the Low Background Chamber (LBC), with 20g of low background Skipper CCDs, has been recently installed at Laboratoire Souterrain de Modane and is currently taking data. We will report the status of the DAMIC-M experiment and first results obtained with LBC commissioning data.

/pdf/the-damic-m-experiment-status-and-first-results-3gxzotv6.pdf

The DAMIC-M experiment: Status and first results

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The micro-pattern gas detector PIM: A multi-modality solution for novel investigations in functional imaging

The DAMIC-M experiment: Status and first results