Short-Range Test of the Equivalence Principle

We rotated a 3 ton ²³⁸U attractor around a compact torsion balance and compared the accelerations of Cu and Pb toward U. We found that ${a}Cu{{-}a}Pb{{0ex}{0ex}}={{0ex}{0ex}}({-}0.7±{}5.7)×{}{10}^{{-}13}cm/{s}²$, compared to the $9.8×{}{10}^{{-}5}cm/{s}²$ 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-Z.