Short-range tests of the equivalence principle

We tested the equivalence principle at short length scales by rotating a 3-ton ${}^{238}$U attractor around a compact torsion balance containing Cu and Pb test bodies. The observed differential acceleration of the test bodies toward the attractor, $a_{\text{Cu}}-a_{\text{Pb}}=(1.0\pm 2.8)\times {10}^{-13}$ cm/s${}^2$, should be compared to the corresponding gravitational acceleration of $9.2\times {10}^{-5}$ cm/s${}^2$. Our results set new constraints on equivalence-principle violating interactions with Yukawa ranges down to 1 cm, and improve by substantial factors existing limits for ranges between 10 km and 1000 km. Our data also set strong constraints on certain power law potentials that can arise from two-boson exchange processes.