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

Dual-phase liquid argon detectors measure 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 has the potential to improve the ionization electron electroluminescence signal in multiple ways, including a higher ionization yield thanks to the lower ionization energy of xenon, while maintaining a strong 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 could generate more photons per ionized electron, as well as energy transfer 128 nm Ar2 dimer light to more detectable 149 nm and 175 nm light from Xe excitations. We discuss the deployment of the CHILLAX detector at LLNL, which operates a ~35 g active target dual phase argon detector doped with percent level xenon in the liquid phase. We quantify the increase to the observed light from the electroluminescence signal channel from doping up to 4% xenon concentration (by molar fraction) and propose an analytical model to describe the energy transfer mechanism in argon-xenon gas mixtures. We conclude by discussing undergoing improvements to the system and planned measurements.

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.