title: 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).
authors.affiliation: Department of Physics, University of California Irvine, Irvine, CA 92697-4575, USA rdnewman@uci.edu.
authors.forename: Riley
authors.initials: R
authors.lastname: Newman
authors.affiliation: Department of Physics, University of California Irvine, Irvine, CA 92697-4575, USA ExoAnalytic Solutions Inc., Mission Viejo, CA 92692, USA.
authors.forename: Michael
authors.initials: M
authors.lastname: Bantel
authors.affiliation: Department of Physics, University of California Irvine, Irvine, CA 92697-4575, USA.
authors.forename: Eric
authors.initials: E
authors.lastname: Berg
authors.affiliation: Department of Physics, University of California Irvine, Irvine, CA 92697-4575, USA MongoDB, New York, NY 10036, USA.
authors.forename: William
authors.initials: W
authors.lastname: Cross
keywords: G; Newton's constant; gravitational constant