A Scintillating Xenon Bubble Chamber for Dark Matter Detection

A wealth of cosmological observations indicate that our universe is 27% cold, non-baryonic dark matter. While the nature of dark matter is unknown, the leading candidate is an as-yet undiscovered weakly interacting massive particle (WIMP), which should be observable in terrestrial detectors through elastic scattering with atomic nuclei. The PICO Collaboration (formerly COUPP and PICASSO) is one of many groups working to unambiguously detect this signal. The bubble chamber technique employed by PICO shares the strong background discrimination and easy scalability of other leading dark matter detection technologies, but has the unique feature that it is not restricted to a particular target material – any superheated fluid can serve as a dark matter target. PICO already uses the ability to change targets to search separately for spin-dependent and spin-independent WIMP couplings and for high- and low-mass WIMPs, but there is potential to take further advantage this flexibility by adopting a scintillating fluid as the target. This proposal will support the construction and operation of a prototype scintillating xenon bubble chamber for dark matter detection. The addition of scintillation will address the weak point of the bubble chamber technique (lack of energy information), while the choice of xenon as a target forges a direct link to other xenon dark matter detectors, allowing for cross-calibrations of detector response and a direct comparison of any observed signal. This sort of cross-technology comparison will be a crucial part of any future dark matter discovery.