Unveiling the hidden: the quest for dark matter particles
Forecast of DAMIC-M 90% CL limit on the DM-electron cross section for a light dark photon model. An improvement of several orders of magnitude over previous limits is expected, which will exclude the hypothesis that all DM in the universe is made of this particular candidate (orange line).
Our understanding of the laws governing the universe has advanced enormously during the last few decades, moving from a blurry picture to the realm of precision cosmology. Indeed, observations of the sky with powerful telescopes have unequivocally established dark matter (DM) and dark energy as preponderant components of the universe. Dark matter is five times more abundant than ordinary matter, and has an enormous influence – for example, making our Sun move much faster in the Milky Way. But its true nature is unknown.

Some theorize that DM is composed of a new class of particles – the so-called weakly interacting massive particles (WIMPs) – relics of the primordial thermal bath of the early universe. WIMPs are implied by extensions of the Standard Model of particle physics such as supersymmetry. These models suggest WIMPs of 100s GeV mass, or hundreds of billions of electron-volts. Experimental searches for DM have been strongly motivated by the WIMP paradigm. The detection principle is common to all experiments: a WIMP scatters off a nucleus of ordinary matter like a billiard ball, and the recoiling nucleus leaves a tiny energy deposit in the detector. To screen the detector from the overwhelming cosmic ray flux, experiments are located in deep underground laboratories. So far WIMPs have eluded detection. Also, no evidence for the supporting supersymmetry theory has yet been found at the Large Hadron Collider, the world’s most powerful particle accelerator.

The scientific community is re-evaluating the WIMP paradigm, recognizing that DM particles may be lighter and have different interaction properties than previously thought. In particular, a dark photon – an invisible, massive version of the ordinary photon – could be a fundamental component of DM, or act as mediator of DM interactions. Candidates for particles in this so-called dark or hidden sector span over a large range of masses, down to the single electron-volt, and are largely unconstrained by current experiments.

DAMIC-M is uniquely suited to search for these candidates which, contrary to WIMPs, can also interact with electrons in the target material. With a detection threshold as low as two electrons and the lowest leakage current ever achieved in a silicon detector, DAMIC-M will explore the hidden sector with unprecedented sensitivity.