A measurement of G with a cryogenic torsion pendulum

Abstract

A measurement of Newton's gravitational constant G has been made with a cryogenic torsion pendulum operating below 4 K in a dynamic mode in which G is determined from the change in torsional period when a field source mass is moved between two orientations. The source mass was a pair of copper rings that produced an extremely uniform gravitational field gradient, whereas the pendulum was a thin fused silica plate, a combination that minimized the measurement's sensitivity to error in pendulum placement. The measurement was made using an as-drawn CuBe torsion fibre, a heat-treated CuBe fibre, and an as-drawn Al5056 fibre. The pendulum operated with a set of different large torsional amplitudes. The three fibres yielded high Q -values: 82 000, 120 000 and 164 000, minimizing experimental bias from fibre anelasticity. G -values found with the three fibres are, respectively: {6.67435(10),6.67408(15),6.67455(13)}×10 −11 m 3 kg −1 s −2 , with corresponding uncertainties 14, 22 and 20 ppm. Relative to the CODATA2010 G -value, these are higher by 77, 37 and 107 ppm, respectively. The unweighted average of the three G -values, with the unweighted average of their uncertainties, is 6.67433(13)×10 −11 m 3 kg −1 s −2 (19 ppm).

Recent measurements of the gravitational constant as a function of time

“…Three types of fibers with differing mechanical properties, especially amplitude dependence of the mechanical losses, were used. A result for each fiber was published in 2014 [2]: G = (6.674 35 ± 0.000 10) × 10 −11 m 3 kg −1 s −2 , G = (6.674 08 ± 0.000 15) × 10 −11 m 3 kg −1 s −2 , and G = (6.674 55 ± 0.000 13) × 10 −11 m 3 kg −1 s −2 . The principal investigator provided the following time information: Data with the first fiber was first were obtained from Oc- LENS-14: Following pioneering work at Stanford University [27], a precision measurement of G using a vertical atom interferometer was performed at the University of Florence, Italy.…”

Progress in Precise Measurements of the Gravitational Constant

“…In 2014, three new G values were added in the latest adjustment, which are named as BIPM‐14, UCI‐14, and LENS‐14 . The BIPM‐14 is an improvement determination of G that based on their previous experiment performed in 2001, and the UCI‐14 is a measurement of G using a cryogenic torsion pendulum below 4 K with the time‐of‐swing method, and the LENS‐14 is a completely new measurement with atom interferometry, which has the totally different systematic error sources.…”

Measurement of the Newtonian constant of gravitation G by precision displacement sensors

“…Measurements of fundamental constants of physics have been one of the most important work in the field of metrology. Over time, more and more precise measurements have been achieved [1], affecting the definition of the units [2]. Typically, these constants are measured with relative precisions around 10 −7 or better.…”