Heavy, Multi-Scattering dark matter particles in DEAP-3600

DEAP-3600 is the largest running direct detection experiment with 3.3 tonnes of liquid argon. The detector, located 2 km underground at SNOLAB, is primarily designed to search for Weakly Interacting Massive Particles (WIMPs). Besides WIMPs, noble liquid detectors can also be sensitive to super-massive dark matter candidates, up to the Planck scale. These dark matter candidates might have been produced non-thermally, like in inflaton decays mechanisms, or as radiation from primordial black holes, as well as extended thermal production in a dark sector. Specifically, dark matter candidates with masses above 10^{16} GeV and cross-sections in argon above 10^{-24} cm^2, can also reach underground detectors like DEAP-3600. Their large cross-section means that they produce a sequence of collinear nuclear recoils as they traverse the detector, resulting in a signal that is distinct from both WIMPs and backgrounds. This characteristic formed the basis of a dedicated analysis searching for heavy, multi-scattering dark matter.  

The high quality of the selection cuts and the knowledge of the already modeled backgrounds allowed for the definition of three different Regions of Interest (ROIs), each with a background level of less than one event. After unblinding three years of data talking, no events were found in the Regions of Interest, leading to world-leading constraints on two composite dark matter models, up to Planck-scale masses.