Optimal detectors for WIMP and 0–ν ββ searches: Identical high-pressure xenon gas TPCs?

A time projection chamber (TPC) filled with high-pressure gaseous xenon (HPXe)—instead of liquid xenon (LXe)—appears likely to offer both superior energy resolution for the 0–ν ββ decay search in 136Xe and superior γ-background rejection in the search for WIMPs. An augmentation to maximize the primary scintillation detection efficiency of the 0–ν ββ decay detector design will realize an optimum design for both purposes. In this scenario an attractive synergy exists: two identical HPXe TPCs differing only in isotopic content will provide significantly more robust evidence for the existence of either signal if present. A simple analysis of important factors that limit energy resolution leads to the conclusion that the optimal design for either next-generation search at the few hundred kg level is the same HPXe-based TPC. A careful measurement of the scintillation and ionization responses of HPXe to nuclear and electronic recoils is needed to test the claim of HPXe superiority to LXe for the combined goals.