First Direct Detection Constraints on Planck-Scale Mass Dark Matter with Multiple-Scatter Signatures Using the DEAP-3600 Detector

Dark matter with Planck-scale mass (≃10¹⁹ GeV /c² ) arises in well-motivated theories and could be produced by several cosmological mechanisms. A search for multiscatter signals from supermassive dark matter was performed with a blind analysis of data collected over a 813 d live time with DEAP-3600, a 3.3 t single-phase liquid argon-based detector at SNOLAB. No candidate signals were observed, leading to the first direct detection constraints on Planck-scale mass dark matter. Leading limits constrain dark matter masses between 8.3 ×10⁶ and 1.2 ×10¹⁹ GeV /c² , and Ar 40 -scattering cross sections between 1.0 ×10⁻²³ and 2.4 ×10⁻¹⁸ cm² . These results are interpreted as constraints on composite dark matter models with two different nucleon-to-nuclear cross section scalings.