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PRL 100, 041101 (2008) PHYSICAL REVIEW LETTERS
week ending 1 FEBRUARY 2008 Test of the Equivalence Principle Using a Rotating Torsion Balance
S. Schlamminger, K.-Y. Choi, T. A. Wagner, J. H. Gundlach, and E. G. Adelberger
Center for Experimental Nuclear Physics and Astrophysics, University of Washington, Seattle, Washington, 98195, USA (Received 4 October 2007; revised manuscript received 3 December 2007; published 28 January 2008) 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 aN;Be-Ti
0:6 3:1 10ÿ15 m=s2 improves limits on equivalence-principle violations with ranges from 1 m to 1 ¨¨ by an order of magnitude. The Eotvos parameter is Earth;Be-Ti
0:3 1:8 10ÿ13 . 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 DM;Be-Ti
ÿ4 7 10ÿ5 . Space-ﬁxed differential accelerations in any direction are limited to less than 8:8 10ÿ15 m=s2 with 95% conﬁdence.
DOI: 10.1103/PhysRevLett.100.041101 PACS numbers: Galileo’s
of the apparatus and Figure 1 shows a schematic drawing The equivalence of gravitational mass and inertial mass Earth
is assumed as one of the most fundamental principles in nature. Practically every theoretical attempt to connect general relativity to the standard model allows for a violation of the equivalence principle . Equivalence-principle tests are therefore important tests of uniﬁcation scale physics far beyond the reach of traditional particle physics experiments. The puzzling discoveries of dark matter and dark energy provide strong motivation to extend tests of the equivalence principle to the highest precision possible. Over the past two decades we have conducted laboratory tests of the equivalence principle [2 – 5]. This Letter reports our latest and most precise measurement using a new, Eric
the 70.3 g pendulum. The pendulum body is a thin aluminum shell with fourfold azimuthal symmetry and up down reﬂection symmetry. It carries four beryllium and four titanium test masses in a horizontal dipole conﬁguration. These two materials were chosen primarily to maximize the difference in baryon number (B= is 0.998 68 for Be and 1.001 077 for Ti), and secondly for experimental reasons, such as densities, magnetic properties, and machinability. The Ti test bodies are hollow to match the external shape and mass of the 4.84 g Be test bodies to within 50 g. The test-body shape allows us to reproducibly interchange the test bodies, to minimize alignment errors, ...
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