G measurements with time-of-swing method at HUST

Precision measurement of the Newtonian gravitational constant

The Newtonian gravitational constant G, which is one of the most important fundamental physical constants in nature, plays a significant role in the fields of theoretical physics, geophysics, astrophysics and astronomy. Although G was the first physical constant to be introduced in the history of science, it is considered to be one of the most difficult to measure accurately so far. Over the past two decades, eleven precision measurements of the gravitational constant have been performed, and the latest recommended value for G published by the Committee on Data for Science and Technology (CODATA) is (6.674 08 ± 0.000 31) × 10-11 m3 kg-1 s-2 with a relative uncertainty of 47 parts per million. This uncertainty is the smallest compared with previous CODATA recommended values of G; however, it remains a relatively large uncertainty among other fundamental physical constants. In this paper we briefly review the history of the G measurement, and introduce eleven values of G adopted in CODATA 2014 after 2000 and our latest two values published in 2018 using two independent methods.

Test of the Equivalence Principle with Chiral Masses Using a Rotating Torsion Pendulum

Here we present a new test of the equivalence principle designed to search for the possible violation of gravitational parity using test bodies with different chiralities. The test bodies are a pair of left- and right-handed quartz crystals, whose gravitational acceleration difference is measured by a rotating torsion pendulum. The result shows that the acceleration difference towards Earth Δa_{left-right}=[-1.7±4.1(stat)±4.4(syst)]×10^{-15}  m s^{-2} (1-σ statistical uncertainty), correspondingly the Eötvös parameter η=[-1.2±2.8(stat)±3.0(syst)]×10^{-13}. This is the first reported experimental test of the equivalence principle for chiral masses and opens a new way to the search for the possible parity-violating gravitation.

Measurements of the gravitational constant using two independent methods

The Newtonian gravitational constant, G, is one of the most fundamental constants of nature, but we still do not have an accurate value for it. Despite two centuries of experimental effort, the value of G remains the least precisely known of the fundamental constants. A discrepancy of up to 0.05 per cent in recent determinations of G suggests that there may be undiscovered systematic errors in the various existing methods. One way to resolve this issue is to measure G using a number of methods that are unlikely to involve the same systematic effects. Here we report two independent determinations of G using torsion pendulum experiments with the time-of-swing method and the angular-acceleration-feedback method. We obtain G values of 6.674184 × 10^-11 and 6.674484 × 10^-11 cubic metres per kilogram per second squared, with relative standard uncertainties of 11.64 and 11.61 parts per million, respectively. These values have the smallest uncertainties reported until now, and both agree with the latest recommended value within two standard deviations.

Influence of tungsten fiber's slow drift on the measurement of G with angular acceleration method

In the measurement of the gravitational constant G with angular acceleration method, the equilibrium position of torsion pendulum with tungsten fiber undergoes a linear slow drift, which results in a quadratic slow drift on the angular velocity of the torsion balance turntable under feedback control unit. The accurate amplitude determination of the useful angular acceleration signal with known frequency is biased by the linear slow drift and the coupling effect of the drifting equilibrium position and the room fixed gravitational background signal. We calculate the influences of the linear slow drift and the complex coupling effect on the value of G, respectively. The result shows that the bias of the linear slow drift on G is 7 ppm, and the influence of the coupling effect is less than 1 ppm.

Research on supporting mounts of spheres in measurement of gravitational constant G

The ongoing precision measurement of the gravitational constant G at our group is performed by using two different kinds of methods: time-of-swing method (ToS) and angular acceleration feedback method. In the two methods, the stainless steel spheres are employed as source masses, and the position stability of the spheres is an important parameter, which make suitable mounts for supporting the spheres needed extremely. In this paper, an upgraded three-point mount is introduced and tested in detail. Experimental results show that, for the sphere supported by the three-point mount used in the ToS method, the repeatability, the temperature influence, and the vibration influence are all less than 0.1 μm (about 2 ppm for the value of G). For the sphere supported by the three-point mount used in the AAF method, similar results are obtained, the largest change of the sphere's position is about 0.6 μm, introduced by a temperature change of 1 °C, which also results in an uncertainty of 2 ppm for the value of G.

Influence of temperature on period of torsion pendulum with a high-Q fused silica fiber

Due to the high-Q fused silica fiber's extreme sensitivity to temperature change, the period estimation of torsion pendulum with high precision depends on the effective correction of the thermoelastic effect. In the measurement of G with the time-of-swing method, we analyze the complex relation between temperature and the pendulum's period and propose a developed method to find the shear thermoelasticity coefficient as well as isolate the influence of temperature on period alone. The result shows that the shear thermoelasticity coefficient is 101(2) × 10(-6)/°C, the resultant correction to Δ(ω(2)) is 9.16(0.18) ppm, and the relative uncertainty to G is less than 1 ppm.