Bulletin of the American Physical Society
2007 APS April Meeting
Volume 52, Number 3
Saturday–Tuesday, April 14–17, 2007; Jacksonville, Florida
Session C12: Experimental Tests of Gravity |
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Sponsoring Units: GGR Chair: Stephen H. Merkowitz, NASA Goddard Space Flight Center Room: Hyatt Regency Jacksonville Riverfront City Terrace 8 |
Saturday, April 14, 2007 1:30PM - 2:06PM |
C12.00001: Improved Test of the Equivalence Principle Invited Speaker: We present results for the most precise lab test of the equivalence principle to date. Our experiment uses a torsion pendulum with beryllium and titanium test bodies arranged in a composition dipole and is mounted on a turntable that rotates with constant angular velocity. A violation of the equivalence principle would result in a differential acceleration of the two materials toward a source mass. We measure a differential acceleration of $1 \pm 6 \times 10^{-15}\; m/s^2$ and analyze our data toward a variety of source masses allowing us to constrain the violation of the equivalence principle for ranges of one meter to infinity. In collaboration with Todd Wagner, Ki-Young Choi, Jens Gundlach, and Eric Adelberger, University of Washington. [Preview Abstract] |
Saturday, April 14, 2007 2:06PM - 2:18PM |
C12.00002: A New Laboratory Test of the Equivalence Principle Robert Reasenberg, James Phillips To test the Equivalence Principle (EP) to an accuracy of at least $\Delta $g/g = 5 10$^{-14}$, we are developing a modern Galilean experiment. In our principle of equivalence measurement (POEM), we directly examine the relative motion of two vertically separated test mass assemblies (TMA) that are freely falling in a co-moving vacuum chamber. A second pair of TMA, laterally separated from the first and with reversed test-substance locations, mitigates systematic error. Frequent automated lateral interchanges of the TMA further reduces susceptibility to systematic error. There are three key technologies: The laser gauge [RSI \textbf{76}, 064501 (2005)], which measures the separation of the TMA to picometer accuracy, was developed over a decade ago and has recently been enhanced; The motion system, which launches the TMA from their kinematic mounts inside the chamber and keeps the chamber on a trajectory that mimics free fall, is working and receiving a major upgrade; And the capacitance gauge system, which measures an additional four kinematic degrees of freedom of each TMA, is near completion at the Rowland Institute at Harvard. We will describe the operation and status of POEM, its error budget and expected accuracy, and recent results. [Preview Abstract] |
Saturday, April 14, 2007 2:18PM - 2:30PM |
C12.00003: Lessons Learned from Gravity Probe B for STEP, LISA and other experiments Paul Worden, Saps Buchman Demanding experiments such as GP-B require not only scientific expertise from the investigators but also the ability to quickly recognize and adapt to a wide variety of unexpected scientific, technical and programmatic difficulties, from minor discrepancies to design flaws and outright failures. GP-B provides several excellent examples of the process of recovery from these events which are of interest to developing missions. Flexible design and planning are part of the recovery process, but a clear understanding of the programmatic environment is required to have a good chance of success. Specific technical lessons in the areas of materials and fabrication technology, mission architecture and operations, as well as integrated test systems including hardware and software are presented. We also describe examples of GP-B flight anomalies with particular relevance to STEP and LISA that should be avoided in the future, thus enhancing reliability for these missions. [Preview Abstract] |
Saturday, April 14, 2007 2:30PM - 2:42PM |
C12.00004: Proper Motion of the GP-B Guide Star Irwin Shapiro, Daniel Lebach, Michael Ratner, Norbert Bartel, Ryan Ransom, Michael Bietenholz, Jerusha Lederman, Jean-Francois Lestrade We discuss Gravity Probe B's (GP-B's) guide star: the process for its selection, the determination of its proper motion, and the error analysis of the resultant estimate. With the Stanford GP-B team, we chose an optically-bright binary system, IM Peg (HR 8703), as the guide star. This system emits radio radiation, thus allowing us to determine IM Peg's proper motion with respect to extremely distant radio sources. In each of 35 sessions of 8.4~GHz VLBI observations spread between 1997 and mid 2005, we obtained the sky position of IM Peg's radio emission, relative to 2, and sometimes 3, extragalactic radio sources nearby on the sky. We detail the random and systematic errors in these position determinations and give our final value of the standard error in the resultant estimate of IM Peg's proper motion. This standard error is less than our project-specified goal of 0.15 milliarcseconds per year. We will not disclose our value for IM Peg's proper motion until the GP-B data analysis is completed, since this GR test is to be as (nearly) ``double blind'' as feasible. [Preview Abstract] |
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