Research On The Tilt And Magnetic Field Effects In Equivalence Principle Test Experiment Based On Torsion Balance Under The Aim Of 10^-14

The equivalence principle refers to the universal phenomenon of the acceleration of test mass’s free fall in a gravitational field independent of its internal structure and composition,which is a basis of Einstein’ s general relativity.However,general relativity is not compatible with the standard models that describe quantum physics.Most theoretical models that attempt to unify gravity with the other three fundamental interactions predict new interactions and new "particles",invoking some form of equivalence principle violation.Therefore,high-precision experimental test of the equivalent principle can not only help people have a better understanding of the nature of gravity,but also can play a role to explore "new physics".For high-precision experimental testing of the equivalence principle,our team use the rotating torsion balance to test the equivalence principle by adopting different chiral objects at the precision of η～4×10-13 for the first time in the world,which is almost equal to the best level on earth.The system effects of tilt coupling,magnetic coupling,and gravitational gradient coupling in experiments are all limiting factors under the test target with higher precision.During my Ph.D.period,I carried out a series of studies and finished the following works:(1)To reduce the effect caused by the tilt of the rotation axis,the active feedback control method is adopted to compensate the real-time inclination of the rotation axis.The tilt we are concerned about is reduced to the level of several nanoradians,and the tilt effect is η=0.52(3)× 10-13.(2)To reduce the magnetic field effect,we use the simulation design aided method to design a magnetic shield with a higher shielding factor.The newly designed magnetic shield with a horizontal geomagnetic field shielding factor up to 1.9×106 is complete and the magnetic field shielding factor improved about 200 times.The magnetic effect contributes to E(?)tv(?)s parameter η=1.0(0.7)× 10-15.(3)To reduce the coupling of the gravitational gradient effect,we not only redesign a higher symmetrical pendulum but also compensate the background gravity gradient with well-crafted mass sources.As a result,the q21Q21 coupling and q41Q41 coupling contribute to E(?)tv(?)s parameter η=4.1(0.8)×10-13 and η=0.0(1.0)× 10-13.Besides,by upgrading the speed control system and algorithm,the speed noise of the turntable at the concerned frequency is reduced to<1 × 10-11 rad·s-1/(?),with a reduced factor about 100 times.The suppression of these systematic effects and random noise lays a foundation for the test of equivalence principle for the goal of η～10-14.