Short-range tests of the equivalence principle

We tested the equivalence principle at short length scales by rotating a 3 ton ²³⁸U attractor around a compact torsion balance containing Cu and Pb test bodies. The observed differential acceleration of the test bodies toward the attractor, a_Cu-a_Pb=(1.0+/-2.8)×10^-13 cm/s², should be compared to the corresponding gravitational acceleration of 9.2×10^-5 cm/s². 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.