Riley Newman

Recent measurements of the gravitational constant as a function of time

A recent publication (J.D. Anderson et. al., EPL 110, 1002) presented a strong correlation between the measured values of the gravitational constant

High precision measurement of torsion fiber internal friction at cryogenic temperatures

G

A measurement of G with a cryogenic torsion pendulum

and the 5.9-year oscillation of the length of day. Here, we provide a compilation of all published measurements of

LABORATORY TESTS OF GRAVITATIONAL PHYSICS USING A CRYOGENIC TORSION PENDULUM

G

Gravitation physics at BGPL

taken over the last 35 years. A least squares regression to a sine with a period of 5.9 years still yields a better fit than a straight line. However, our additions and corrections to the G data reported by Anderson {\it et al.} significantly weaken the correlation.

Measurements of torsion fiber anelastic properties in preparation for a new measurement of G

Cryogenic torsion pendulums being developed for research in gravitational physics serve well for exceptionally accurate measurements of nonlinear and anelastic properties of torsion fibers at low temperature (77 K and 4.2 K) at low frequency (|0.01 Hz) in a pre-plastic regime of high shear strain (0.0001-0.003). The measurements use a torsion pendulum suspended by a thin fiber (typically|20 mm324 cm), oscillating with an amplitude of many revolutions. In a few oscillation cycles, oscillation amplitude and frequency may be 8 determined to better than one part in 10 , and harmonic deviations from simple harmonic motion (at 77 K) with fractional accuracy better 29 than 10 , enabling very accurate determination of the decrement, modulus defect, and hysteresis loop of the system as a function of oscillation amplitude.

Experimental tests of the gravitational inverse-square law for mass separations from 2 to 105 cm.

A measurement of Newtons 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 measurements 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 m3 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 m3 kg−1 s−2 (19 ppm).

Test of the Gravitational Inverse-Square Law at Laboratory Distances

Progress and plans are reported for a program of gravitational physics experiments using cryogenic torsion pendula undergoing large amplitude torsional oscillation. The program includes a UC Irvine project to measure the gravitational constant G and joint UC Irvine - U. Washington projects to test the gravitational inverse square law at a range of about 10 cm and to test the weak equivalence principle.

On determining G using a cryogenic torsion pendulum

Abstract We report progress on a program of gravitational physics experiments using cryogenic torsion pendula undergoing large-amplitude torsion oscillation. This program includes tests of the gravitational inverse square law and of the weak equivalence principle. Here, we describe our ongoing search for inverse-square-law violation at a strength down to 10−5 of standard gravity. The low-vibration environment provided by the Battelle Gravitation Physics Laboratory (BGPL) is uniquely suited to this study.

Constraining the couplings of massive pseudoscalars using gravity and optical experiments

We present results of measurements of anelastic properties of CuBe and Al5056 torsion fibers at low temperature, and discuss their implications for a planned measurement of G using a cryogenic torsion pendulum. It appears that anelastic behavior should not limit a G measurement at a level of a few ppm.