We are continuing our search for violations of the inverse
square law using a torsion pendulum with 21-fold rotational
symmetry to probe gravity to distances below 100 microns.
New Eot-Wash limits on the strength of Yukawa interactions
with ranges between 50 microns and 1 cm will be presented.
[D9.002] A Tabletop Test of Gravity at sub-100~\mum Distances
Sylvia Smullin, Andrew Geraci, David Weld (Stanford University Department of Physics), John Chiaverini (National Institute of Standards and Technology, Boulder), Aharon Kapitulnik (Stanford University Department of Physics)
Recent theories of TeV physics have generated much interest
in tests for deviations from Newtonian gravity at distances
of less than 1~mm. Predictions of extra dimensions and other
physics beyond the Standard Model include Yukawa-type
modifications to the classical Newtonian gravitation
potential at length scales and magnitudes that may be
accessible in tabletop experiments. We have built a probe to
measure gravity-like forces on the order of 10^-18~N at
distances of less than 100~\mum.(J. Chiaverini,
S. J. Smullin, A. A. Geraci, D. M. Weld, A. Kapitulnik,
Phys. Rev. Lett. 90, 151101 (2003).) The force sensor is a
silicon cantilever to which is attached a gold test mass.
The drive mass is a pattern of alternating gold and silicon
bars, which is oscillated below the test mass at a
subharmonic of the cantilever resonant frequency. This talk
will describe the experiment and our results.
[D9.003] Searching for New Physics from 20 microns to a micron and below
Andrew Geraci, Sylvia Smullin, David Weld, Aharon Kapitulnik, Savas Dimopoulos (Department of Physics, Stanford University)
Several recent theoretical ideas suggest that new physics
related to gravity may appear at short length scales. For
example, light moduli or particles in "large" extra
dimensions could mediate macroscopic forces of
(super)gravitational strength at length scales below a
millimeter. At the 20 microns level, I will discuss the
Stanford cantilever experiment (J. Chiaverini, S.
J. Smullin, A. A. Geraci, D. M. Weld, A. Kapitulnik,
Phys.Rev.Lett. 90, 151101 (2003).), including an improvement
involving a magnetic analog which allows force calibration
and precision alignment to reduce systematics. I will also
discuss some experimental challenges at length scales below
a few microns including the Casimir/Van der Waals
background, and will describe an experimental prospect to
search for new (sub)-micron forces using arrays of trapped
Bose-Einstein condensed atoms (Savas Dimopoulos and
Andrew A. Geraci, Phys. Rev. D 68, 124021 (2003). ).
[D9.004] A New Apparatus for Measuring Gravity-like Forces at Small Length Scales
David Weld, Blas Cabrera, Aharon Kapitulnik (Department of Physics, Stanford University)
This talk will discuss the design and construction of a new
type of cantilever-based probe for measuring gravity-like
forces at length scales of order 10^-5 meters. The
apparatus is based on a cryogenic helium gas bearing with a
hemispherical quartz rotor. The bearing housing contains a
silicon nitride cantilever with a metallic test mass mounted
on the tip. An alternating pattern of high- and low-density
materials is embedded in the flat surface of the rotor so
that when the rotor is spun, the mass on the cantilever is
subjected to an AC gravitational force. This design combines
some of the geometrical advantages of torsion-balance
experiments with the small mass size and force sensitivity
of our previous cantilever-based experiment.(J.
Chiaverini et al., Phys. Rev. Lett. 90 , 151101 (2003))
[D9.005] Weak Equivalence Principle Tests using a Rotating Torsion Balance
Ki-Young Choi, Jens Gundlach, Stephan Schlamminger, Blayne Heckel, Eric Adelberger, Erik Swanson (CENPA. University of Washington)
We are testing the weak equivalence principle using a
rotating torsion balance. A composition dipole, consisting
of titanium and beryllium, is suspended form a torsion
fiber. The whole torsion balance is rotated with a constant
angular velocity about the fiber axis. A violation of the
equivalence principle would result in a periodic
differential acceleration of the two materials directed
towards a large variety of sources. We will be able to test
the equivalence principle for ranges from ~1m to infinity.
In particular we can test for differential accelerations
between the two different materials toward the center of our
galaxy. Since about 25% of the acceleration towards the
center of the galaxy is caused by dark matter, this
measurement allows us to test for the equivalence principle
for the galactic dark matter. We expect to achieve a
differential acceleration sensitivity of
1\times\;10^-15\; \mboxm/\mboxs^2, which will
allow us to test the equivalence principle for galactic dark
matter at the 10^-4 level.
[D9.006] Affine vs. Metric Gravitation Parity Test
Alan M. Schwartz (MGLS, Ltd.)
Gravitation theories are antisymmetric or symmetric to parity transformation. Calculated test mass geometry is a natural challenge of modeled spacetime geometry. Test mass quantitative parity divergence arises from atom coordinates alone, measured on a normalized scale of CHI=0 (achiral) to CHI=1 (perfect parity divergence). Parity Eötvös experiments in unmodified apparatus are proposed contrasting chemically and dimensionally identical \alpha-quartz single crystal test masses in crystallographic space groups P3_121 and P3_221. Both explicit calculation of a 3.34x10^14 atom model and a pure geometric model yield CHI>1-(1.48x10^-16). It is shown that parity Eötvös experiment Equivalence Principle violation is >520 times that allowed for composition experiments, suggesting empirically measurable failure of the weakest general relativity founding postulate.