The GGG differential accelerometer is made of concentric coaxial test cylinders weakly coupled in the horizontal plane and spinning in supercritical regime around their symmetry axis. GGG is built as a full scale ground based prototype for the proposed "Galileo Galilei-GG" space experiment aiming to test the equivalence principle (EP) to 10(-17) at room temperature. We report measured Q values of 95000 at 1.4 Hz, and expect even better ones at typical spin frequencies of a few Hz. An EP violation signal in the field of the Sun would appear as a low frequency displacement in the horizontal plane of the laboratory, and it can be separated out from a much larger whirl motion of the test masses at their natural differential frequency. So far we have managed to reduce the amplitude of this whirl to about 0.1 mum. We discuss how to improve these results in view of the very high accuracy GG experiment in space, and/or to reach a 10(-13) sensitivity in the lab which would allow us to either confirm or rule out recent predictions of violation to this level. (C) 2003 Published by Elsevier B.
