A LABORATORY TEST OF THE EQUIVALENCE PRINCIPLE AS PROLOG TO A SPACEBORNE EXPERIMENT

Abstract

To test the equivalence principle (EP) to an accuracy of at least σ(Δ g)/g = 5 × 10-14, we are developing a modern Galilean experiment. In our principle-of-equivalence measurement (POEM), we directly examine the relative motion of two test mass assemblies (TMA) that are freely falling. Such an experiment tests both for a possible violation of the weak equivalence principle (WEP) and for new forces that might mimic a WEP violation. For the terrestrial version of the experiment, there are three key technologies. A laser gauge measures the separation of the TMA to picometer accuracy in a second as they fall freely in a comoving vacuum chamber. The motion system launches the TMA from their kinematic mounts inside the chamber and keeps the chamber on a trajectory that mimics free fall until the chamber nears the bottom of its motion. It then "bounces" the chamber back to upward motion in preparation for a new launch of the TMA. A capacitance gauge system measures an additional four degrees of freedom of the motion of each TMA. The resulting estimate of the rotation around and translation along the horizontal axes is used to correct systematic errors. We describe the status of POEM and discuss recent progress.