515 research outputs found
Precision measurement of light shifts at two off-resonant wavelengths in a single trapped Ba+ ion and determination of atomic dipole matrix elements
We define and measure the ratio (R) of the vector ac-Stark effect (or light
shift) in the 6S_1/2 and 5D_3/2 states of a single trapped barium ion to 0.2%
accuracy at two different off-resonant wavelengths. We earlier found R =
-11.494(13) at 514.531nm and now report the value at 1111.68nm, R = +0.4176(8).
These observations together yield a value of the matrix element,
previously unknown in the literature. Also, comparison of our results with an
ab initio calculation of dynamic polarizability would yield a new test of
atomic theory and improve the understanding of atomic structure needed to
interpret a proposed atomic parity violation experiment.Comment: 12 pages, 11 figures, in submission to PR
Effects of confinement on the permanent electric-dipole moment of Xe atoms in liquid Xe
Searches for permanent electric-dipole moments (EDM) of atoms provide
important constraints on competing extensions to the standard model of
elementary particles. Recently proposed experiment with liquid Xe [M.V.
Romalis and M.P. Ledbetter, Phys. Rev. Lett. \textbf{87}, 067601 (2001)] may
significantly improve present limits on the EDMs. To interpret experimental
data in terms of CP-violating sources, one must relate measured atomic EDM to
various model interactions via electronic-structure calculations. Here we study
density dependence of atomic EDMs. The analysis is carried out in the framework
of the cell model of the liquid coupled with relativistic atomic-structure
calculations. We find that compared to an isolated atom, the EDM of an atom of
liquid Xe is suppressed by about 40%
Measurement of Linear Stark Interference in 199Hg
We present measurements of Stark interference in the 6
6 transition in Hg, a process whereby a static electric field
mixes magnetic dipole and electric quadrupole couplings into an electric
dipole transition, leading to -linear energy shifts similar to those
produced by a permanent atomic electric dipole moment (EDM). The measured
interference amplitude, = = (5.8 1.5) (kV/cm), agrees with relativistic, many-body predictions and
confirms that earlier central-field estimates are a factor of 10 too large.
More importantly, this study validates the capability of the Hg EDM
search apparatus to resolve non-trivial, controlled, and sub-nHz Larmor
frequency shifts with EDM-like characteristics.Comment: 4 pages, 4 figures, 1 table; revised in response to reviewer comment
Improved limit on the permanent electric dipole moment of 199Hg
We report the results of a new experimental search for a permanent electric
dipole moment of 199Hg utilizing a stack of four vapor cells. We find d(199Hg)
= (0.49 \pm 1.29_stat \pm 0.76_syst) x 10^{-29} e cm, and interpret this as a
new upper bound, |d(199Hg)| < 3.1 x 10^{-29} e cm (95% C.L.). This result
improves our previous 199Hg limit by a factor of 7, and can be used to set new
constraints on CP violation in physics beyond the standard model.Comment: 4 pages, 4 figures. additional reference, minor edits in response to
reviewer comment
Atomic Parity Nonconservation: Electroweak Parameters and Nuclear Structure
There have been suggestions to measure atomic parity nonconservation (PNC)
along an isotopic chain, by taking ratios of observables in order to cancel
complicated atomic structure effects. Precise atomic PNC measurements could
make a significant contribution to tests of the Standard Model at the level of
one loop radiative corrections. However, the results also depend upon certain
features of nuclear structure, such as the spatial distribution of neutrons in
the nucleus. To examine the sensitivity to nuclear structure, we consider the
case of Pb isotopes using various recent relativistic and non-relativistic
nuclear model calculations. Contributions from nucleon internal weak structure
are included, but found to be fairly negligible. The spread among present
models in predicted sizes of nuclear structure effects may preclude using Pb
isotope ratios to test the Standard Model at better than a one percent level,
unless there are adequate independent tests of the nuclear models by various
alternative strong and electroweak nuclear probes. On the other hand,
sufficiently accurate atomic PNC experiments would provide a unique method to
measure neutron distributions in heavy nuclei.Comment: 44 pages, INT Preprint DOE/ER/40561-050-INT92-00-1
Low Metallicity Galaxies from the Dark Energy Survey
We present a new selection of 358 blue compact dwarf galaxies (BCDs) from
5,000 square degrees in the Dark Energy Survey (DES), and the spectroscopic
follow-up of a subsample of 68 objects. For the subsample of 34 objects with
deep spectra, we measure the metallicity via the direct T method using the
auroral [\oiii] 4363 emission line. These BCDs have average oxygen
abundance of 12+log(O/H)= 7.8, stellar masses between 10 to 10
M and specific SFR between 10 to 10 yr. We
compare the position of our BCDs with the Mass-metallicity (M-Z) and
Luminosity-metallicity (L-Z) relation derived from the Local Volume Legacy
sample. We find the scatter around the M-Z relation is smaller than the scatter
around the L-Z relation. We identify a correlation between the offsets from the
M-Z and L-Z relation that we suggest is due to the contribution of metal-poor
inflows. Finally, we explore the validity of the mass-metallicity-SFR
fundamental plane in the mass range probed by our galaxies. We find that BCDs
with stellar masses smaller than M do not follow the
extrapolation of the fundamental plane. This result suggests that mechanisms
other than the balance between inflows and outflows may be at play in
regulating the position of low mass galaxies in the M-Z-SFR space.Comment: 16 pages, 10 figures, submitted to ApJ, We invite comments from the
communit
Constraints on Gamma-ray Emission from the Galactic Plane at 300 TeV
We describe a new search for diffuse ultrahigh energy gamma-ray emission
associated with molecular clouds in the galactic disk. The Chicago Air Shower
Array (CASA), operating in coincidence with the Michigan muon array (MIA), has
recorded over 2.2 x 10^{9} air showers from April 4, 1990 to October 7, 1995.
We search for gamma rays based upon the muon content of air showers arriving
from the direction of the galactic plane. We find no significant evidence for
diffuse gamma-ray emission, and we set an upper limit on the ratio of gamma
rays to normal hadronic cosmic rays at less than 2.4 x 10^{-5} at 310 TeV (90%
confidence limit) from the galactic plane region: (50 degrees < l < 200
degrees); -5 degrees < b < 5 degrees). This limit places a strong constraint on
models for emission from molecular clouds in the galaxy. We rule out
significant spectral hardening in the outer galaxy, and conclude that emission
from the plane at these energies is likely to be dominated by the decay of
neutral pions resulting from cosmic rays interactions with passive target gas
molecules.Comment: Astrophysical Journal, submitted, 11 pages, AASTeX Latex, 3
Postscript figure
Measurement of the Cosmic Ray Energy Spectrum and Composition from 10^{17} to 10^{18.3} eV Using a Hybrid Fluorescence Technique
We study the spectrum and average mass composition of cosmic rays with
primary energies between 10^{17} eV and 10^{18} eV using a hybrid detector
consisting of the High Resolution Fly's Eye (HiRes) prototype and the MIA muon
array. Measurements have been made of the change in the depth of shower maximum
as a function of energy. A complete Monte Carlo simulation of the detector
response and comparisons with shower simulations leads to the conclusion that
the cosmic ray intensity is changing f rom a heavier to a lighter composition
in this energy range. The spectrum is consistent with earlier Fly's Eye
measurements and supports the previously found steepening near 4 \times 10^{17}
eV .Comment: 39 pages, 15 figures, in revtex4 epsf style, submited to AP
A Multi-Component Measurement of the Cosmic Ray Composition Between 10^{17} eV and 10^{18} eV
The average mass composition of cosmic rays with primary energies between
eV and eV has been studied using a hybrid detector consisting
of the High Resolution Fly's Eye (HiRes) prototype and the MIA muon array.
Measurements have been made of the change in the depth of shower maximum,
, and in the change in the muon density at a fixed core location,
, as a function of energy. The composition has also been
evaluated in terms of the combination of and . The
results show that the composition is changing from a heavy to lighter mix as
the energy increases.Comment: 14 pages including 3 figures in revtex epsf style, submited to PR
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