Short-Range Test of the Equivalence Principle

Abstract

We rotated a 3 ton ${}^{238}\mathrm{U}$ attractor around a compact torsion balance and compared the accelerations of Cu and Pb toward U. We found that ${a}_{\mathrm{Cu}}{\ensuremath{-}a}_{\mathrm{Pb}}\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}(\ensuremath{-}0.7\ifmmode\pm\else\textpm\fi{}5.7)\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}13}\mathrm{cm}/{\mathrm{s}}^{2}$, compared to the $9.8\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}5}\mathrm{cm}/{\mathrm{s}}^{2}$ gravitational acceleration toward the attractor. Our results set new constraints on equivalence-principle violating interactions with Yukawa ranges down to 1 cm and rule out an earlier suggestion of a Yukawa interaction coupled predominantly to $N\ensuremath{-}Z$.