Test Of The Weak Equivalence Principle For Chiral Material Using A Rotating Torsion Balance

The weak equivalence principle,which states that any test bodies in a gravitational field fall with the same acceleration independent of their composition and structure,is a basis of Einstein's general relativity.However,most of the theories unifying the gravitation and the other three fundamental interactions predict new interactions as a result of the violation of the weak equivalence principle.Hence,test of the weak equivalence principle is a search for new interactions.Recently,some scientists considered new interactions not only dependent on the composition,but also on the rotation,polarization,spin or chirality,which induces that the test masses with different rotations,polarizations,spins or chiralities in a gravitational field will fall with different accelerations.The acceleration difference between these different test masses have been measured by many experimental groups,except the different chiralities.For the first time,we measured the acceleration difference between the test masses with different chiralities in a gravitational field using a rotating torsion balance.First a precise rotating torsion balance was built.After analyzing and controlling the various noise sources,including the thermal noise related to the internal losses and the gas damping,the twist angle readout noise,the rotation noise and so on,the torque noise floor was suppressed to the level of about 5× 10^{- 15} N ·m ·Hz ^-1/2,very close to the theoretical limit which the system can achieve,which is also the advanced world level.Then we estimated the effects that mimic the signal of interest,including the gravitational field,magnetic field,thermal couplings and the periodic fluctuations of the rotation speed.After we reduced some of these effects,the total uncertainty of them was 2.6× 10 ^-18 N· m.Finally,the frequency of the signal of interest was placed where the signal-to-noise is relatively optimal,and we measured the acceleration difference between the different test masses,left-and right-handed quartz crystals in the horizontal gravitational field of the Earth.The result is?3.5±5.9?× 10^{- 15} m ·s^{- 1/2},corresponding to the E?tv?s parameter ?=?2.4±4.0?×10^-13, close to the best test of the weak equivalence principle on the Earth.