Dark Matter Detector R&D
Rare event searches requires detailed understanding of detector behavior, and as sesitivity increases, previously unobserved instrumental effects become important. The Generation 3 Dark Matter experiments will probe the tails of the distributions that were understood for G2. Our detector R&D work focuses on measuring liquid xenon signal generation, including electron extraction across liquid-gas boundary, photoelectron response of PMTs, few-keV nuclear recoil signal yields, light collection, and parasitic high voltage effects. Many LBNL facilities enable precise investigations, for example metal surface electropolishing and electron microscopy expertise and capabilities. We have recently made a first measurement of double photoelectron response in VUV-sensitive PMTs (Faham et al, JINST 10 P09010) and extended the Lindhard model of nuclear recoil signal quenching to the lowest energies (Sorensen, Phys. Rev. D 91 083509 2015). Our on-going R&D program includes: measurement PMT VUV response at liquid xenon temperature, performing a keV photoneutron nuclear recoil signal yield calibration, which affects low mass WIMP and 8 B neutrino signal interpretation, absolute measurement of extraction of electrons across liquid-gas boundary in liquid noble gas TPCs, studies of high voltage-induced breakdown and electroluminescence in liquid xenon, and optimization of VUV scintillation photon detection, including teflon reflectivity, wavelength shifter efficiency and distribution of reflected/emitted light. Many of these activities have overlap and synergy with neutrino detector R&D.