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Constraints on Light Dark Matter Particles Interacting with Electrons
We report direct-detection constraints on light dark matter particles interacting with electrons. The results are based on a method that exploits the extremely low levels of leakage current of the DAMIC detector at SNOLAB of 2–6×10^-22  A cm^−2. We evaluate the charge distribution of pixels that collect <10e- for contributions beyond the leakage current that may be attributed to dark matter interactions. Constraints are placed on so-far unexplored parameter space for dark matter masses between 0.6 and 100  MeV c^-2. We also present new constraints on hidden-photon dark matter with masses in the range 1.2–30  eV c^-2.
DAMIC-MThe DAMIC (DArk Matter In CCDs) experiment employs a novel technique to search for the elusive particles that we think make up most of the matter in the universe—dark matter.

DAMIC has pioneered the detection of nuclear and electronic recoils induced by dark matter particles in the silicon bulk of charge-coupled devices - the CCDs that have been used for many years in digital cameras and in the focal plane of astronomical telescopes for the digital imaging of faint astrophysical objects. Our unusually thick CCDs - almost a mm compared with the typical tens of microns – are extremely sensitive: they can detect signals as low as few electrons, as those expected from light dark matter interactions. In addition, the spatial resolution of these devices – the pixel size is 15 micron x 15 micron – results in the unique capability to characterize and reject backgrounds from radiogenic sources. This unconventional use of CCDs has been successfully demonstrated by DAMIC at the SNOLAB underground laboratory in Canada where a 40-g prototype detector is currently operating.

A kg-size detector will be installed at the Laboratoire Souterrain de Modane in France, protected from cosmic rays by the rock overburden of the Alps. The DAMIC-M (DAMIC at Modane) experiment will feature the most massive CCDs ever built and a novel concept for signal readout – based on non-destructive, repetitive measurements of the pixel charge – resulting in the high-resolution detection of a single electron. With this unprecedented sensitivity DAMIC-M will take a leap forward of several orders of magnitude in the exploration of the dark matter particle hypothesis, in particular of candidates pertaining to the so-called “hidden sector” which may have well so far escaped detection.