Stephan Schlamminger

Test of the equivalence principle using a rotating torsion balance.

We used a continuously rotating torsion balance instrument to measure the acceleration difference of beryllium and titanium test bodies towards sources at a variety of distances. Our result Deltaa(N),(Be-Ti)=(0.6+/-3.1)x10(-15) m/s2 improves limits on equivalence-principle violations with ranges from 1 m to infinity by an order of magnitude. The Eötvös parameter is eta(Earth,Be-Ti)=(0.3+/-1.8)x10(-13). By analyzing our data for accelerations towards the center of the Milky Way we find equal attractions of Be and Ti towards galactic dark matter, yielding eta(DM,Be-Ti)=(-4+/-7)x10(-5). Space-fixed differential accelerations in any direction are limited to less than 8.8x10(-15) m/s2 with 95% confidence.

Torsion-balance tests of the weak equivalence principle

We briefly summarize motivations for testing the weak equivalence principle and then review recent torsion-balance results that compare the differential accelerations of beryllium–aluminum and beryllium–titanium test-body pairs with precisions at the part in 1013 level. We discuss some implications of these results for the gravitational properties of antimatter and dark matter and speculate about the prospects for further improvements in experimental sensitivity.

New CP-Violation and Preferred-Frame Tests with Polarized Electrons

We used a torsion pendulum containing approximately 9 x 10(22) polarized electrons to search for CP-violating interactions between the pendulums electrons and unpolarized matter in the laboratorys surroundings or the Sun, and to test for preferred-frame effects that would precess the electrons about a direction fixed in inertial space. We find, /g(P)(e)g(S)(N)//(Plancks constant x c) < 1.7 x 10(-36), and /g(A)(e)g(V)(N)//(Plancks constant x c) < 4.8 x 10(-56) for lambda > 1 AU. Our preferred-frame constraints, interpreted in the Kostelecký framework, set an upper limit on the parameter /b(e)/ <or= 5.0 x 10(-21) eV that should be compared to the benchmark value m(e)(2)/M(Planck)= 2 x 10(-17) eV.

Determination of the Planck constant using a watt balance with a superconducting magnet system at the National Institute of Standards and Technology

For the past two years, measurements have been performed with a watt balance at the National Institute of Standards and Technology (NIST) to determine the Planck constant. A detailed analysis of these measurements and their uncertainties has led to the value h = 6.626 069 79(30) × 10−34 J s. The relative standard uncertainty is 45 × 10−9. This result is 141 × 10−9 fractionally higher than h90. Here h90 is the conventional value of the Planck constant given by , where KJ-90 and RK-90 denote the conventional values of the Josephson and von Klitzing constants, respectively.

Temporal Extent of Surface Potentials between Closely Spaced Metals

Variations in the electrostatic surface potential between the proof mass and electrode housing in the space-based gravitational wave mission Laser Interferometer Space Antenna (LISA) is one of the largest contributors of noise at frequencies below a few mHz. Torsion balances provide an ideal test bed for investigating these effects in conditions emulative of LISA. Our apparatus consists of a Au coated Cu plate brought near a Au coated Si plate pendulum suspended from a thin W wire. We have measured a white noise level of 30 microV/sqrt Hz above approximately 0.1 mHz, rising at lower frequencies, for the surface potential variations between these two closely spaced metals.

Construction, Measurement, Shimming, and Performance of the NIST-4 Magnet System

The magnet system is one of the key elements of a watt balance. For the new watt balance currently under construction at the National Institute of Standards and Technology, a permanent magnet system was chosen. We describe the detailed construction of the magnet system, first measurements of the field profile, and shimming techniques that were used to achieve a flat field profile. The relative change of the radial magnetic flux density is <; 10-4 over a range of 5 cm. We further characterize the most important aspects of the magnet and give order of magnitude estimates for several systematic effects that originate from the magnet system.

Design of the Permanent-Magnet System for NIST-4

A new watt balance, i.e., NIST-4, is currently being designed at the National Institute of Standards and Technology. This apparatus will be used to realize the unit of mass after the redefinition of the kilogram has taken effect. In order to ensure smooth operation at regular mass realizations, the watt balance should be easy to use and reliable. To meet these requirements, a permanent-magnet system will be implemented to generate the magnetic flux required to operate NIST-4. A brief overview of the permanent-magnet system and its design considerations are given.

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

The watt or Kibble balance: a technique for implementing the new SI definition of the unit of mass

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A summary of the Planck constant measurements using a watt balance with a superconducting solenoid at NIST

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