652 research outputs found
Limit on the Temporal Variation of the Fine-Structure Constant Using Atomic Dysprosium
Over a period of eight months, we have monitored transition frequencies
between nearly degenerate, opposite-parity levels in two isotopes of atomic
dysprosium (Dy). These transition frequencies are highly sensitive to temporal
variation of the fine-structure constant () due to relativistic
corrections of large and opposite sign for the opposite-parity levels. In this
unique system, in contrast to atomic-clock comparisons, the difference of the
electronic energies of the opposite-parity levels can be monitored directly
utilizing a radio-frequency (rf) electric-dipole transition between them. Our
measurements show that the frequency variation of the 3.1-MHz transition in
Dy and the 235-MHz transition in Dy are 9.06.7 Hz/yr and
-0.66.5 Hz/yr, respectively. These results provide a value for the rate of
fractional variation of of yr (1
) without any assumptions on the constancy of other fundamental
constants, indicating absence of significant variation at the present level of
sensitivity.Comment: 4 pages, 2 figure
New experimental limits on non-Newtonian forces in the micrometer-range
We report measurements of the short-range forces between two macroscopic
gold-coated plates using a torsion pendulum. The force is measured for
separations between 0.7 m and 7 m, and is well described by a
combination of the Casimir force, including the finite-temperature correction,
and an electrostatic force due to patch potentials on the plate surfaces. We
use our data to place constraints on the Yukawa-type "new" forces predicted by
theories with extra dimensions. We establish a new best bound for force ranges
0.4 m to 4 m, and, for forces mediated by gauge bosons propagating in
dimensions and coupling to the baryon number, extract a
-dimensional Planck scale lower limit of TeV.Comment: 4 pages, 2 figure
Neutron Moderation in the Oklo Natural Reactor and the Time Variation of alpha
In the analysis of the Oklo (gabon) natural reactor to test for a possible
time variation of the fine structure constant alpha, a Maxwell-Boltzmann low
energy neutron spectrum was assumed. We present here an analysis where a more
realistic spectrum is employed and show that the most recent isotopic analysis
of samples implies a non-zero change in alpha, over the last two billion years
since the reactor was operating, of \Delta\alpha/\alpha\geq 4.5\times 10^{-8}
(6\sigma confidence). Issues regarding the interpretation of the shifts of the
low energy neutron resonances are discussed.Comment: 7 pages, 4 figures; version 2 included reference to Flambaum/Shuryak
work and corrects error in abstract version three corrects a few points and
adds discussion on hydrogen and impurity concentration
Variation of the Fine-Structure Constant and Laser Cooling of Atomic Dysprosium
Radio-frequency electric-dipole transitions between nearly degenerate,
opposite parity levels of atomic dysprosium (Dy) were monitored over an
eight-month period to search for a variation in the fine-structure constant,
. The data provide a rate of fractional temporal variation of
of yr or a value of for , the variation coefficient for in a changing
gravitational potential. All results indicate the absence of significant
variation at the present level of sensitivity. We also present initial results
on laser cooling of an atomic beam of dysprosium.Comment: 10 pages, 6 figures, fixed typos in section 5, updated result
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