Short-Range Test of the Equivalence Principle

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 $a_{\mathrm{Cu}}{-a}_{\mathrm{Pb}}=(-0.7\mathrm{}\pm 5.7)\times {10}^{-13\mathrm{}}\mathrm{cm}/{\mathrm{s}}^2$, compared to the $9.8\times {10}^{-5\mathrm{}}\mathrm{cm}/{\mathrm{s}}^2$ 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 $N-Z$.