Recent Results of a Xenon-Doped Argon Ionization Detector with the CHILLAX Experiment

Two-phase liquid argon detectors measure ionization signals by detecting electroluminescence light produced by ionization electrons extracted from liquid into gas under a strong electric field. Xenon-doping of argon at the few percent level in the liquid phase improves the electroluminescence signal in multiple ways, including a higher ionization yield thanks to the lower ionization energy of xenon, while maintaining a superior kinetic match to light targets (e.g. neutrinos and light dark matter candidates) compared with pure xenon. Percent level doping in liquid populates xenon in the gas phase at the 10s of ppm level, which can generate more photons per ionized electron, as well as wavelength shift 128 nm Ar2 dimer light to more detectable 149 nm and 178 nm light from ArXe and Xe2 dimers, respectively. We discuss the most recent runs of the CHILLAX experiment at LLNL, which operates a ~50 g active target dual phase argon detector doped with percent level xenon in the liquid phase. We describe early measurements of the improvement to the electroluminescence signal channel as a function of increasing xenon concentration.

This work was performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory (LLNL) under Contract DE-AC52-07NA27344.