New Test of the Equivalence Principle from Lunar Laser Ranging

Abstract

An analysis of six years of lunar-laser-ranging data gives a zero amplitude for the Nordtvedt term in the Earth-Moon distance yielding the Nordtvedt parameter $\ensuremath{\eta}=0.00\ifmmode\pm\else\textpm\fi{}0.03$ Thus, Earth's gravitational self-energy contributes equally, \ifmmode\pm\else\textpm\fi{}3%, to its inertial mass and passive gravitational mass. At the 70% confidence level this result is only consistent with the Brans-Dicke theory for $\ensuremath{\omega}>29$. We obtain $|\ensuremath{\beta}\ensuremath{-}1|\ensuremath{\lesssim}0.02 \mathrm{to} 0.05$ for five-parameter parametrized post-Newtonian theories of gravitation with energy-momentum conservation, or $|\ensuremath{\beta}\ensuremath{-}1|\ensuremath{\lesssim}0.01$ if only $\ensuremath{\beta}$ and $\ensuremath{\gamma}$ are considered.