Benchmarking Air Light-Guide Cherenkov Detectors at SLAC ESTB

The MOLLER experiment proposed at the Thomas Jefferson National Accelerator Facility plans a precision low energy determination of the weak mixing angle via the measurement of the parity-violating asymmetry in longitudinally polarized beam electron scattering on the unpolarized electrons in a liquid hydrogen target (Møller scattering). The scattered electrons are measured by a circular array of thin fused silica tiles which generate Cherenkov photons and transport them to photomultiplier tubes (PMTs) through air light-guides. The detector design must balance constraints of machining, structural support, maximizing the PMTs' optical photon yield and resolution, and minimizing the backgrounds from neighboring separated fluxes. Prior tests at the MAMI facility at Johannes Gutenberg University, Mainz, Germany characterized the effects of Cherenkov and scintillation light generated by flux passing through the air of the detectors' light guides. We report on tests performed at the SLAC End Station A Test Beam (ESTB), Geant4 optical physics simulations, and ongoing studies of optimized detector geometry prototypes for the MOLLER experiment.