Benjamin Roberts (U. of Queensland)

3:30pm Wednesday March 30, 2022

Dark matter induced atomic ionisation

Weakly interacting massive particles (WIMPs) have long been a favoured dark matter candidate, though repeated null results in direct detection experiments are quickly narrowing the parameter space in which they may be hiding. Lighter WIMPs, with masses below that of typical atomic nuclei, are far less constrained. Such WIMPs are typically too light to leave appreciable nuclear recoils, but may be detected via their scattering off atomic electrons. Determining the observable event rates for this scenario involves calculating atomic ionisation cross sections, which turns out to be less simple than naively expected, with relativistic and other collective atomic effects playing a significant role. Importantly, we demonstrate that the potential scintillation event rate can be much larger than otherwise expected, meaning that competitive searches can be performed for ~GeV scale WIMPs using the conventional direct detection experiments. I’ll discuss implications for current and upcoming experiments, including the recently observed excess in the low-energy electron recoils at xenon 1T experiment.