36,173 research outputs found
Radio-frequency spectroscopy of weakly bound molecules in spin-orbit coupled atomic Fermi gases
We investigate theoretically radio-frequency spectroscopy of weakly bound
molecules in an ultracold spin-orbit-coupled atomic Fermi gas. We consider two
cases with either equal Rashba and Dresselhaus coupling or pure Rashba
coupling. The former system has been realized very recently at Shanxi
University [Wang et al., arXiv:1204.1887] and MIT [Cheuk et al.,
arXiv:1205.3483]. We predict realistic radio-frequency signals for revealing
the unique properties of anisotropic molecules formed by spin-orbit coupling.Comment: 11 pages, 7 figure
Observation of Bs->Ds(*)+Ds(*)- using e+e- collisions and a determination of the Bs-Bsbar width difference \Delta\Gamma_s
We have made the first observation of Bs->Ds(*)+Ds(*)- decays using 23.6 fb-1
of data recorded by the Belle experiment running on the Upsilon(5S) resonance.
The branching fractions are measured to be B(B^0_s\ra D^+_s D^-_s) =
(1.0\,^{+0.4}_{-0.3}\,^{+0.3}_{-0.2})%, B(B^0_s\ra D^{*\pm}_s D^{\mp}_s) =
(2.8\,^{+0.8}_{-0.7}\,\pm 0.7)%, and B(B^0_s\ra D^{*+}_s D^{*-}_s) =
(3.1\,^{+1.2}_{-1.0}\,\pm 0.8)%; the sum is B(B^0_s\ra D^{(*)+}_s D^{(*)-}_s) =
(6.9\,^{+1.5}_{-1.3}\,\pm 1.9)%. Assuming Bs->Ds(*)+Ds(*)- saturates decays to
CP-even final states, the branching fraction determines the ratio
\Delta\Gamma_s/cos(\phi), where \Delta\Gamma_s is the difference in widths
between the two Bs-Bsbar mass eigenstates, and \phi is a CP-violating weak
phase. Taking CP violation to be negligibly small, we obtain
\Delta\Gamma_s/\Gamma_s =
0.147^{+0.036}_{-0.030}(stat.)^{+0.044}_{-0.042}(syst.), where \Gamma_s is the
mean decay width.Comment: 13 pages, 2 figures, 2 tables. v2: text added for clarification,
version published in Phys. Rev. Letter
The Spectral Energy Distributions of White Dwarfs in 47 Tucanae: The Distance to the Cluster
We present a new distance determination to the Galactic globular cluster 47
Tucanae by fitting the spectral energy distributions of its white dwarfs to
pure hydrogen atmosphere white dwarf models. Our photometric dataset is
obtained from a 121 orbit Hubble Space Telescope program using the Wide Field
Camera 3 UVIS/IR channels, capturing F390W, F606W, F110W, and F160W images.
These images cover more than 60 square arcmins and extend over a radial range
of 5-13.7 arcmin (6.5-17.9 pc) within the globular cluster. Using a likelihood
analysis, we obtain a best fitting unreddened distance modulus of (m -
M)o=13.36+/-0.02+/-0.06 corresponding to a distance of 4.70+/-0.04+/-0.13 kpc,
where the first error is random and the second is systematic. We also search
the white dwarf photometry for infrared excess in the F160W filter, indicative
of debris disks or low mass companions, and find no convincing cases within our
sample.Comment: Accepted to The Astronomical Journal, 13 Figures, 2 Tables. Figures 3
and 6 are figure sets, each composed of 59 subfigures (to appear in the
electronic journal). This is a Companion paper to the article ID:
submit/037561
A laser based accelerator for ultracold atoms
We present first results on our implementation of a laser based accelerator
for ultracold atoms. Atoms cooled to a temperature of 420 nK are confined and
accelerated by means of laser tweezer beams and the atomic scattering is
directly observed in laser absorption imaging. The optical collider has been
characterized using Rb87 atoms in the |F=2,mF=2> state, but the scheme is not
restricted to atoms in any particular magnetic substates and can readily be
extended to other atomic species as well.Comment: (c) 2012 The Optical Society, 3 pages, 4 figures, 1 movie lin
Dynamic spin response of a strongly interacting Fermi gas
We present an experimental investigation of the dynamic spin response of a
strongly interacting Fermi gas using Bragg spectroscopy. By varying the
detuning of the Bragg lasers, we show that it is possible to measure the
response in the spin and density channels separately. At low Bragg energies,
the spin response is suppressed due to pairing, whereas the density response is
enhanced. These experiments provide the first independent measurements of the
spin-parallel and spin-antiparallel dynamic and static structure factors and
open the way to a complete study of the structure factors at any momentum. At
high momentum the spin-antiparallel dynamic structure factor displays a
universal high frequency tail, proportional to , where is the probe energy.Comment: Replaced with final versio
Pulsar data analysis with PSRCHIVE
PSRCHIVE is an open-source, object-oriented, scientific data analysis
software library and application suite for pulsar astronomy. It implements an
extensive range of general-purpose algorithms for use in data calibration and
integration, statistical analysis and modeling, and visualisation. These are
utilised by a variety of applications specialised for tasks such as pulsar
timing, polarimetry, radio frequency interference mitigation, and pulse
variability studies. This paper presents a general overview of PSRCHIVE
functionality with some focus on the integrated interfaces developed for the
core applications.Comment: 21 pages, 5 figures; tutorial presented at IPTA 2010 meeting in
Leiden merged with talk presented at 2011 pulsar conference in Beijing;
includes further research and development on algorithms for RFI mitigation
and TOA bias correctio
The heating of dust by old stellar populations in the Bulge of M31
We use new Herschel multi-band imaging of the Andromeda galaxy to analyze how
dust heating occurs in the central regions of galaxy spheroids that are
essentially devoid of young stars. We construct a dust temperature map of M31
through fitting modified blackbody SEDs to the Herschel data, and find that the
temperature within 2 kpc rises strongly from the mean value in the disk of 17
pm 1K to \sim35K at the centre. UV to near-IR imaging of the central few kpc
shows directly the absence of young stellar populations, delineates the radial
profile of the stellar density, and demonstrates that even the near-UV dust
extinction is optically thin in M31's bulge. This allows the direct calculation
of the stellar radiation heating in the bulge, U\ast(r), as a function of
radius. The increasing temperature profile in the centre matches that expected
from the stellar heating, i.e. that the dust heating and cooling rates track
each other over nearly two orders of magnitude in U\ast. The modelled dust
heating is in excess of the observed dust temperatures, suggesting that it is
more than sufficient to explain the observed IR emission. Together with the
wavelength dependent absorption cross section of the dust, this demonstrates
directly that it is the optical, not UV, radiation that sets the heating rate.
This analysis shows that neither young stellar populations nor stellar near-UV
radiation are necessary to heat dust to warm temperatures in galaxy spheroids.
Rather, it is the high densities of Gyr-old stellar populations that provide a
sufficiently strong diffuse radiation field to heat the dust. To the extent
which these results pertain to the tenuous dust found in the centres of
early-type galaxies remains yet to be explored.Comment: 11 pages. Accepted for publication in MNRA
Halpha Equivalent Widths from the 3D-HST survey: evolution with redshift and dependence on stellar mass
We investigate the evolution of the Halpha equivalent width, EW(Halpha), with
redshift and its dependence on stellar mass, taking advantage of the first data
from the 3D-HST survey, a large spectroscopic Treasury program with the Hubble
Space Telescope WFC3. Combining our Halpha measurements of 854 galaxies at
0.8<z<1.5 with those of ground based surveys at lower and higher redshift, we
can consistently determine the evolution of the EW(Halpha) distribution from
z=0 to z=2.2. We find that at all masses the characteristic EW(Halpha) is
decreasing towards the present epoch, and that at each redshift the EW(Halpha)
is lower for high-mass galaxies. We measure a slope of EW(Halpha) ~ (1+z)^(1.8)
with little mass dependence. Qualitatively, this measurement is a
model-independent confirmation of the evolution of star forming galaxies with
redshift. A quantitative conversion of EW(Halpha) to sSFR is very model
dependent, because of differential reddening corrections between the continuum
SED and the Balmer lines. The observed EW(Halpha) can be reproduced with a
simple model in which the SFR for galaxies rises to the epoch of z~2.5 and then
decreases with time to z = 0. The model implies that the EW(Halpha) rises to
400 A at z=8. The sSFR evolves faster than EW(Halpha), as the mass-to-light
ratio also evolves with redshift. In this context, we find that the sSFR
evolves as (1+z)^(3.2), nearly independent of mass, consistent with previous
reddening insensitive estimates. We confirm previous results that the observed
slope of the sSFR-z relation is steeper than the one predicted by models, but
models and observations agree in finding little mass dependence.Comment: 7 pages, 4 Figures, 1 Table. Accepted for publication in ApJ Letter
Laser frequency locking by direct measurement of detuning
We present a new method of laser frequency locking in which the feedback
signal is directly proportional to the detuning from an atomic transition, even
at detunings many times the natural linewidth of the transition. Our method is
a form of sub-Doppler polarization spectroscopy, based on measuring two Stokes
parameters ( and ) of light transmitted through a vapor cell. This
extends the linear capture range of the lock loop by up to an order of
magnitude and provides equivalent or improved frequency discrimination as other
commonly used locking techniques.Comment: 4 pages, 4 figures Revte
Many-body quantum dynamics of polarisation squeezing in optical fibre
We report new experiments that test quantum dynamical predictions of
polarization squeezing for ultrashort photonic pulses in a birefringent fibre,
including all relevant dissipative effects. This exponentially complex
many-body problem is solved by means of a stochastic phase-space method. The
squeezing is calculated and compared to experimental data, resulting in
excellent quantitative agreement. From the simulations, we identify the
physical limits to quantum noise reduction in optical fibres. The research
represents a significant experimental test of first-principles time-domain
quantum dynamics in a one-dimensional interacting Bose gas coupled to
dissipative reservoirs.Comment: 4 pages, 4 figure
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