Short-range tests of the equivalence principle

We tested the equivalence principle at short length scales by rotating a 3 ton ${}^{238}\mathrm{U}$ attractor around a compact torsion balance containing Cu and Pb test bodies. The observed differential acceleration of the test bodies toward the attractor, $a_{\mathrm{Cu}}-a_{\mathrm{Pb}}=(1.0\mathrm{}\pm 2.8)\times {10}^{-13}\hspace{0.5em}{\mathrm{c}\mathrm{m}/\mathrm{s}}^2,$ should be compared to the corresponding gravitational acceleration of $9.2\times {10}^{-5}\hspace{0.5em}{\mathrm{c}\mathrm{m}/\mathrm{s}}^2.$ 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.