Probing low-mass WIMP candidates of dark matter with tetrafluoroethane superheated liquid detectors

Abstract: Probing low mass (sub-GeV -- few GeV) Weakly Interacting Massive Particle (WIMP) candidates of dark matter through WIMP-induced nuclear recoils in direct detection experiments requires use of detector materials consisting of low mass target nuclei and low threshold energy. Here we explore the potential of superheated liquid detectors (SLD) with a hydrogen containing liquid, namely, tetrafluoroethane (C${2}$H${2}$F${4}$) (b.p.~$-26.3^\circ\,$C), as the target material for probing low mass WIMPs. It is found that few-keV level recoil energy thresholds possible for bubble nucleation by WIMP-induced $^{12}$C and $^{19}$F recoils in C${2}$H${2}$F${4}$ SLDs operated at atmospheric pressure and gamma-ray insensitive temperatures of $T\, \lesssim\, 35^\circ\,$C have the potential to allow WIMPs in the few-GeV mass range to be probed at a WIMP-nucleon spin-independent cross section sensitivity levels (90% C.L.) better than $4.6\times 10^{-5}\,$pb at WIMP masses down to $\sim$ 4 GeV with a total exposure of $\sim$ 1000 kg.day, provided that the ``thermodynamic efficiency" $\eta_{\rm T}$ that determines the bubble nucleation thresholds for the recoiling nuclei in C${2}$H${2}$F${4}$ is $\sim$ 50% or higher. Sensitivity to sub-GeV WIMP masses generally requires the detector to be sensitive to the WIMP-induced $^1$H recoils, which in turn requires the detector to be operated at temperatures $T\gtrsim 50^\circ\,$C and $\eta{\rm T}$ close to 100%. At such relatively high temperatures (at atmospheric pressure), however, the detector would be sensitive to background gamma rays.