We have measured the gravitational constant, G, with a relative uncertainty of \pm14 ppm. Our new method was designed to minimize systematic uncertainties. A torsion balance was installed on a slowly rotating turntable located between a set of attractor spheres. The rotation rate of the turntable was varied so that the gravitational torque did not twist the torsion fiber and therefore complex properties of the torsion fiber, which had led to a bias in other measurements, were eliminated. The amplitude of the sinusoidal turntable acceleration was measured and is proportional to G. The geometry of our pendulum was a thin flat vertical plate, which made our measurement practically independent of the pendulum mass distribution. Traditionally the pendulum metrology had been one of the largest uncertainties. The attractor masses were located on a second, co-axial, turntable that was rotated with a constant angular velocity difference relative to the pendulum turntable. This allowed us to discriminate against attractions to other objects in the lab. Choosing a high difference velocity and therefore a high signal frequency reduced 1/f-noise.
Our value for Newton's constant is G = (6.674215\pm 0.000092) 10^-11 m^3kg^-1s^-2. When combining our value with results from the LAGEOS satellites the Earth's mass is: M_earth = (5.972245\pm 0.000082) 10^24 kg.
Supported with NIST precision measurement grant #
60NANB7D0053 and NSF grant # PHY-9602494.
[J9.002] Sub-millimeter Tests of the Gravitational Inverse-square Law
C.D. Hoyle (University of Washington), Eotwash Group Team
Motivated by higher-dimensional theories that predict new
effects, we tested the gravitational inverse-square law at
separations ranging down to 218 micrometers using a 10-fold
symmetric torsion pendulum and a rotating 10-fold symmetric
attractor. We improved previous short-range constraints by
up to a factor of 1000 and find no deviations from Newtonian
physics. I will also discuss a second-generation experiment
designed to investigate the gravitational interaction at
even shorter distances. The new apparatus has 26-fold
rotational symmetry and will attain pendulum to attractor
separations of 100 micrometers.
[J9.003] Gravitational Experiment Below 1 Millimeter and Search for Extra-Dimensional Effects
Joshua Long, Allison Churnside, John Price (University of Colorado, Boulder CO)
Gravitational experiments and searches for new macroscopic
forces are only beginning explore distance ranges below 1
millimeter. This region is of rapidly increasing
experimental interest given a number of recent predictions
of new effects, including the possible signatures of
millimeter-scale extra dimensions. An experiment in our
laboratory, using 1 kilohertz mechanical oscillators as test
masses, has been in operation for one year and is designed
to be sensitive to much of the parameter space covered by
these predictions. We review the basic design and
experimental backgrounds, and present our most recent
results.
[J9.004] Testing Scalar-Tensor Gravity using Space Gravitational-Wave Interferometers
Paul D. Scharre, Clifford M. Will (Washington University, St. Louis)
We calculate the bounds which could be placed on
scalar-tensor theories of gravity by measurements of
gravitational waveforms from inspiralling binaries. Systems
of interest are those detectable by LISA, the proposed space
laser interferometric observatory, specifically neutron
stars (NS) spiralling into supermassive black holes (SMBH).
Observation of these systems by LISA may allow for
significantly more stringent bounds on the scalar-tensor
coupling parameter ømega than are achievable from solar
system or binary pulsar measurements. For NS-SMBH
collisions, dipole gravitational radiation modifies the
inspiral, and generates an additional term in the phasing of
the emitted gravitational waveform. Bounds on ømega can
therefore be found by using the technique of matched
filtering. We compute the Fisher information matrix for a
waveform accurate to second post-Newtonian order, including
the effect of dipole radiation, and determine the bounds on
omega for several different NS-SMBH canonical systems.
[J9.005] Extension of Sagnac Calibration to Broadband LISA GW Signals
Peter L. Bender (Univ. of Colorado), Craig J. Hogan (Univ. of Washington)
Armstrong, Estabrook and Tinto have presented particularly
useful observables that can be formed from the 6 main
signals obtainable during the planned ESA/NASA GW mission
LISA. They recently pointed out how one of these called zeta
can be used to calibrate the instrumental noise level for
frequencies below about 3 mHz, where the background of
unresolved galactic binary signals will be higher than the
instrumental noise level. We will describe extension of this
approach to higher frequencies by strong smoothing of the
corrected GW background. Zeta actually corresponds to a
symmetrized version of the Sagnac observables, and its
square determines the mean square of the instrumental noise
for the 6 main LISA signals. The mean square of 3 other
observables (X, Y and Z) has the same property, so much of
its noise can be removed for frequencies of roughly 5 to 20
mHz. This is done frequency by frequency, and the results
are then smoothed to improve the accuracy. With this
approach, the total extragalactic binary background near 10
mHz should be observable.
[J9.006] Constraining sources and theories with gravitational wave observations
James Graber (ICS)
Expressing gravitational wave predictions in terms of
post-Newtonian parameters facilitates the perturbative
computation of alternative possibilities. Similar parametric
techniques can be used to explore the effects of differing
sources (e.g. an accretion disk or an ADAF surrounding a
black hole) and the effects of alternative theories of
gravity. After gravitational waves have been observed, these
same formulas can be used to constrain the theoretical
parameters as a function of the values and uncertainties of
the observed results. We here report on progress in
re-expressing gravitational wave results in parametric form,
add give one example of their possible application. Using
these parametric expressions, and some simplifying
assumptions, we compute that in a favorable case, (a 10
solar mass black hole spiraling in to a 10^6 solar mass
black hole), LISA will be able to constrain at the 10% level
or better a single combination of post-post-Newtonian
parameters one order higher than those already constrained
by solar system evidence. This significant constraint will
be possible, even if the signal to noise level is so low
that the signal can only be found by matched filtering, and
only deviations between alternate signal interpretations of
order one half cycle or more can be detected.
[J9.007] Unequal arm gravitational wave interferometers
Shane L. Larson, William A. Hiscock (Montana State University), Ronald W. Hellings (Jet Propulsion Laboratory)
Unlike ground-based gravitational wave interferometers,
space-based systems such as LISA will not be rigid
structures, and the armlengths will change with time. In the
case where the length of the arms in the interferometer can
vary, it is not possible to use a standard interferometer
signal because the major source of noise in the instrument,
namely laser phase noise, does not cancel out. Using the
method of Tinto and Armstrong, a more complicated signal can
be constructed where laser phase noise exactly cancels out
in an unequal arm interferometer. We will examine the case
where the ratio of the armlengths is a variable parameter,
and demonstrate that this ratio has important consequences
for the overall sensitivity of the observatory.
[J9.008] Angular Fluctuations of Mirrors at LIGO
Biplab Bhawal (LIGO-Caltech), Gabriela Gonzalez (The Pennsylvania State University), David Ottaway (LIGO-Hanford), Tiffany Summerscales (The Pennsylvania State University)
The LIGO (Laser Interferometer Gravitational-Wave
Observatory) is currently being built in the pursuit of
detecting gravitational waves. LIGO consists of three laser
interferometric detectors, two in Hanford Washington and the
other in Livingston, Louisiana. The detectors use mirrors
suspended in pendulums. In November 2000 data was taken with
a preliminary configuration of the interferometer at LIGO
Hanford. Presented here are the results of the Mirror
Angular Fluctuations Study conducted during the run. This
study explored both the amount of angular motion of the
mirrors when free of feedback and the amount of coupling
between interferometer signals and angular mirror motion.
[J9.009] Measurement of Motion Transfer Functions for Mirror Suspensions
Amber Stuver (Penn State), Mark Beilby (Willamette), Aran Glancy, Gabriela Gonzalez (Penn State)
Interferometric gravitational wave detectors, such as LIGO, use mirrors suspended in pendulums. The current LIGO dectors use simple pendulums, but advanced LIGO detectors will use multiple pendulums with some stages on soft vertical springs. A drawback of the a multiple pendulum design is that it is difficult to model and predict cross couplings from one vibrational mode to another due to slight unavoidable asymmetries in the real system. Of most concern are the couplings to motion along the optical axis and into angular motions, which have the most potential to contaminate data.
Our research focuses on the experimental testing of the pendulum designs for cross couplings with a special dedicated shaking stage. The cross couplings in each degree of freedom, their isolation and damping are investigated in this research though the measurement of transfer functions as filtered though the suspension system.
This research is supported by The Pennsylvania State
University, the NSF Grant no. PHY-9870032, and the REU
program at The Pennsylvania State University.
[J9.010] A directional analysis of environmental signals in gravitational wave detectors
Gabriela Gonzalez (Center for Gravitational Physics and Geometry, The Pennsylvania State University)
In gravitational wave detectors such as LIGO, there are many environmental signals and some interferometer signals that have directional information. We develop a method ("beam analysis") to discover such information, and apply it to seismic noise at the LIGO Hanford site. Using this method, we can find out the direction of approach, as well as the transverse or longitudinal characteristics of the seismic waves. We show the application of these results to the analysis of gravitational gradients influencing the interferometer. We also propose the use of this method in some of the interferometric signals.
This work was supported by The Pennsylvania State University
and by the National Science Foundation awards PHY-9973783
and PHY-9870032.
[J9.011] Testing the Gaussianity of Gravitational-Wave Detector Noise
Lee Samuel Finn, Gabriela Gonzalez, Patrick Sutton (Center for Gravitational Physics and Geometry, Penn State)
An important part of the process of data analysis is the
preparation of the data, and a critical part of this process
is the removal of detector artifacts and the
characterization of the residual. Here we describe a test of
the Gaussianity of time-series data and its implementation
in the LIGO gravitational wave detector data monitoring
tool. This test, which relies on the Rayleigh character of
the amplitude of the Fourier transform of a segment of
Gaussian noise, isolates non-Gaussian noise character to
specific sub-bands. Isolating the non-Gaussian noise to a
sub-band permits its removal via an appropriate linear
filter in addition to providing important diagnostic
information for tracking down the source of the excess
noise.
[J9.012] Scalar Gravity Waves from Neutron Stars
Stephen Fairhurst, Lee Samuel Finn, Joshua L. Willis, Jacek Wisniewski (Center for Gravitational Physics and Geometry, Department of Physics, The Pennsylvania State University, University Park, PA 16802, USA)
Distorted rotating neutron stars are good candidates for
sources of gravitational waves, which can be detected in the
near future. Working within the framework of Brans-Dicke
generalization of GR, we calculate the form of such
radiation and the response of an interferometric detector.
Then, we analyze the possibility of placing a lower bound on
the Brans-Dicke constant based on such measurements. Also,
we propose how to obtain information about distortion and
orientation of the star. The statistical analysis of the
signal in the presence of noise is outlined. Finally,
numerical simulations (with LIGO II noise spectrum) provide
estimates for the values of parameters we can expect for
different sources.
[J9.013] Physics and Astrophysics from Distorted Pulsars
Stephen Fairhurst, Lee Samuel Finn, Joshua L. Willis, Jacek Wisniewski (Center for Gravitational Physics and Geometry, Department of Physics, The Pennsylvania State University, University Park, PA 16802, USA)
Distorted rotating neutron stars are good candidates for sources of gravitational waves, which can be detected in the near future. Working within the framework of Brans-Dicke generalization of GR, we calculate the form of such radiation and the response of an interferometric detector. Then, we analyze the possibility of placing a lower bound on the Brans-Dicke constant based on such measurements. Also, we propose how to obtain information about distortion and orientation of the star. The statistical analysis of the signal in the presence of noise is outlined. Finally, numerical simulations (with LIGO II noise spectrum) provide estimates for the values of parameters we can expect for different sources.