Short-range tests of the equivalence principle

Abstract

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, ${a}_{\mathrm{Cu}}\ensuremath{-}{a}_{\mathrm{Pb}}=(1.0\ifmmode\pm\else\textpm\fi{}2.8)\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}13} {\mathrm{c}\mathrm{m}/\mathrm{s}}^{2},$ should be compared to the corresponding gravitational acceleration of $9.2\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}5} {\mathrm{c}\mathrm{m}/\mathrm{s}}^{2}.$ 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.