The Weak Equivalence Principle (WEP) and the General Relativity Accuracy Test (GreAT) with an Einstein Elevator

Abstract - The experiment GReAT (General Relativity Accuracy Test) aims at testing the Weak Equivalence Principle with a precision of several parts in 10^15. The test will be performed by using a cryogenic differential accelerometer consisting of two test masses of different materials, released from a stratospheric altitude to free fall inside an evacuated capsule. The detector is spun about its horizontal axis to modulate the possible violation signal. As a result, the signal will appear at the spin frequency while the effects due to the diagonal components of the gravity gradient tensor in case of imperfect coincidence of the two proof masses centers of mass will appear at twice the rotation frequency