DAMIC-M · Unveiling the Hidden: A Search for Light Dark Matter with CCDs

Dark matter (DM) is a ubiquitous yet invisible presence in our universe. It dictated how galaxies formed in the first place, and now moves stars around them at puzzling speeds. The DM mass in the universe is known to be five times that of ordinary matter; yet its true nature remains elusive. Weakly interacting massive particles (WIMPs), relics from the early universe, are a compelling explanation chased by sensitive experiments in deep underground laboratories. However, searches for heavy WIMPs (≈100 times the proton mass), the most theoretically natural candidates, have been so far unsuccessful. Nor has evidence for such heavy particles yet been found at the CERN Large Hadron Collider. Alternative scenarios are now under scrutiny, such as the existence of a hidden sector of lighter DM particles that interact, differently than WIMPs, also with electrons. DAMIC-M (Dark Matter In CCDs at Modane) will search beyond the heavy WIMP paradigm by detecting nuclear recoils and electrons induced by light DM in charge-coupled devices (CCDs). The 0.5 kg detector will be installed at the Laboratoire Souterrain de Modane, France. In this novel and unconventional use of CCDs, which are commonly employed for digital imaging in astronomical telescopes, the ionization charge will be detected in the most massive CCDs ever built with exquisite spatial resolution (15 μm x 15 μm pixel). The crucial innovation in these devices is the non-destructive, repetitive measurement of the pixel charge, which results in the high-resolution detection of a single electron and unprecedented sensitivity to light DM (≈ eV energies are enough to free an electron in silicon). By counting individual charges in a detector with extremely low leakage current – a combination unmatched by any other DM experiment – DAMIC-M will take a leap forward of several orders of magnitude in the exploration of the hidden sector, a jump that may be rewarded by serendipitous discovery.