LXe purity monitor for the nEXO experiment

The nEXO experiment will search for neutrinoless double beta (0νββ) decay using a 5-tonne liquid xenon (LXe) time projection chamber (TPC), enriched to 90% in Xe136, with a projected half-life sensitivity > 10²⁸ years after 10 years of livetime. The observation of lepton number non-conserving 0νββ decay would imply new physics and require neutrinos to be Majorana fermions. With a general overview of the nEXO experiment, we present tests carried out in LXe at Stanford of a new purity monitor. The measure of the energy of events relies on both the scintillation light and the collection of drifting ionization electrons. The presence of electronegative impurities in the LXe leads to the loss of the drifting electrons through attachment to the dissolved electronegative contaminants. This effect directly impacts our energy resolution, required to be at or below 1%. The nEXO collaboration put in place various strategies to test materials. The Stanford lab designed and built a new purity monitor to measure the concentration of electronegative species emanated by materials considered for nEXO.