TEST OF THE WEAK-EQUIVALENCE PRINCIPLE IN AN EINSTEIN ELEVATOR

A technique for testing the weak-equivalence principle is presented. T his technique involves the measurement of differential accelerations b etween two test masses of different materials (e.g., aluminum and gold ) free falling inside a 3 m long cryostat dropped from a 40 km altitud e balloon. The free-fall duration is 30 s for a non-propelled cryostat . The falling test masses are part of a high-sensitivity differential detector with a foreseeable sensitivity in detecting differential acce lerations of about 1.5.10(-13) g/root Hz (at the liquid-nitrogen tempe rature of 77 K) and 1.5.10(-14) g/root Hz (at the liquid-helium temper ature of 4 K). The detector is spun about a horizontal axis at a frequ ency of typically I Hz in order to modulate the gravity signal duping free fall. The estimated accuracies, with 95% confidence level, in tes ting the weak-equivalence principle in a 30 s integration time are 5 p arts in 10(14) at the temperature of liquid nitrogen and 5 parts in 10 (15) at the temperature of liquid helium.