Using a Wavelength Shifter to Enhance the Sensitivity of Liquid Xenon Dark Matter Detectors

Liquid xenon dark matter detectors have been successfully employed to search for WIMPs, a proposed dark matter candidate. Increasing the scintillation wavelength from 175 nm to 300-400 nm can increase light collection and consequently improve sensitivity to dark matter. Such a shift increases the reflectivity of common reflector materials, decreases the amount of Rayleigh scattering and boosts the quantum efficiency of photomultiplier tubes. In this paper, we show that depositing p-terphenyl (p-TP) solid wavelength shifter on PTFE reflectors and the entrance window of a photomultiplier tube enhanced light-collection efficiency by 21%. We also observed an anti-correlation between the liquid xenon temperature and electron drift length, indicating that the p-TP dissolves into liquid xenon with a temperature dependent solubility. Possible ways to solve the drift length problem are discussed in the paper.