Direct Search for Ultra-light Dark Matter with Torsion Balances

Recent theoretical work has motivated ultra-light bosonic dark matter with masses as small as 10^-22 eV. Our previous torsion-balance equivalence-principle tests have placed limits on the static forces mediated by such bosons between normal test and source masses. (B-L)-coupled vector dark matter would produce a time-varying composition-dependent differential acceleration detectable in our torsion balance instruments. Using fused silica torsion fibers, we have significantly improved the statistical noise of our torsion balance. We have taken data that will set new limits on (B-L)-coupled dark matter candidates in the mass range 5x10^-18 - 5x10^-16 eV.