Improved Determination Of The Newtonian Gravitational Constant G Using The Angular Acceleration Feedback Method

The Newtonian gravitational constant G is one of the earliest fundamental constants in-troduced by human beings.Newton formulated a description of the gravitational interaction in 1687,and the first G value was obtained based on the famous Cavendish’s torsion pendu-lum experiment in 1798.In spite of more than 200 measurement results having been obtained during the past 200 years,G still remains the least precisely known among all fundamental physical constants yet.According to the CODATA-2014 adjustment,some research groups claimed that their measurement uncertainty of G values could reach the level of 10^-5,but their coincidence was one order of magnitude worse.In order to explain the situation,many physicists believe that there are still some systematic effects undiscovered or not evaluated correctly in part or even all the G measurement.In an attempt to find out the possible hidden systematic effects,two new independent determinations of G using torsion pendulum experiments with the time-of-swing method and the angular acceleration feedback method have been conducted in our laboratory since 2009.I participated in the determination of G with the angular acceleration feedback method in my doctoral research,and carried out a series of research work:（1）I participated in building the experimental device for the determination of G with the angular acceleration feedback method,and completed the measurement or the repeated measurement of most experimental parameters;（2）The magnetic damper was redesigned and remade,and the correction con-tributed by the magnetic damper was reduced from 455.40（1.95）ppm to 25.74（8）ppm;（3）Three layers of magnetic shielding were used to enclose the torsion pendulum,hence the un-certainty introduced by the magnetic effect was reduced from 3.98 ppm to 0.90 ppm;（4）The co-moving background gravity gradient created by the rotating shelf was directly compen-sated using a set of specially fabricated copper and aluminium blocks.After compensation,the co-moving background gravity gradient effect was reduced from 1195（9）ppm to less than 2 ppm;（5）The uncertainty introduced by the angle encoders of two turntables was evaluated to be 0.72 ppm.After finishing the above work,I conducted 15 sets of G measurement experiments with the angular acceleration feedback method,and the statistical error of the measurement results was 1.34 ppm.These 15 sets of measurement results were then combined with 14 sets of measurement results obtained by other group members,and the final measurement result is G=6.674484（78）×10^-11m³kg^-1s^-2 with a relative uncertainty of 11.61 ppm,which has the smallest uncertainty reported up to now.