Pictorial image showing, superimposed to an optical image, the spatial distributions of ordinary matter (pink) and the one assigned to dark matter (blue) estimated studying the merging of two clusters of galaxies (Bullet Cluster)

The DarkSide collaboration is an international affiliation of universities and labs seeking to directly detect dark matter in the form of Weakly Interacting Massive Particles (WIMPs). The collaboration is building a series of noble liquid time projection chambers (TPCs) that are designed to be employed at the Gran Sasso National Laboratory in Assergi, Italy. The technique is based on liquid argon depleted in radioactive isotope ³⁹Ar which is common for the atmospheric argon.

Dark-matter seekers get help from the DarkSide

Darkside

As part of the DarkSide program of direct dark matter searches using liquid argon TPCs, a prototype detector with an active volume containing 10 kg of liquid argon, DarkSide-10, was built and operated underground in the Gran Sasso National Laboratory in Italy. A critically important parameter for such devices is the scintillation light yield, as photon statistics limits the rejection of electron-recoil backgrounds by pulse shape discrimination. We have measured the light yield of DarkSide-10 using the readily-identifiable full-absorption peaks from gamma ray sources combined with single-photoelectron calibrations using low-occupancy laser pulses. For gamma lines of energies in the range 122-1275 keV, we get consistent light yields averaging 8.887\pm0.003(stat)\pm0.444(sys) p.e./keV_ee. With additional purification, the light yield measured at 511 keV increased to 9.142\pm0.006(stat) p.e./keV_ee. See:
Light Yield in DarkSide-10: a Prototype Two-phase Liquid Argon TPC for Dark Matter Searches