  The performance of a two-phase Ar avalanche detector with CsI photocathode
was studied, with regard to potential application in coherent neutrino-nucleus
scattering and dark matter search experiments. The detector comprised a 1 cm
thick liquid Ar layer and a triple-GEM multiplier operated in the saturated
vapor above the liquid phase; the CsI photocathode was deposited on the first
GEM. Successful detection of both primary scintillation and ionization signals,
produced by beta-particles in liquid Ar, has for the first time been
demonstrated in the two-phase avalanche mode.
