4,923 research outputs found
QCD corrections to Upsilon production via color-octet states at the Tevatron and LHC
The NLO QCD corrections to Upsilon production via S-wave color-octet states
Upsilon(^1S_0^8,^3S_1^8) at the Tevatron and LHC is calculated. The K factors
of total cross section (ratio of NLO to LO) are 1.313 and 1.379 for
Upsilon(^1S_0^8) and Upsilon(^3S_1^8) at the Tevatron, while at the LHC they
are 1.044 and 1.182, respectively. By fitting the experimental data from the
D0, the matrix elements for S-wave color-octet states are obtained. And new
predictions for Upsilon production are presented. The prediction for the
polarization of inclusive Upsilon contains large uncertainty rising from the
polarization of Upsilon from feed-down of chi_b. To further clarify the
situation, new measurements on the production and polarization for direct
Upsilon are expected.Comment: 13 pages, 10 Figure
The masses and residues of doubly heavy spin--3/2 baryons
The masses and residues of the spin--3/2 doubly heavy baryons are calculated
within the QCD sum rules method. A comparison of our predictions with those
existing in the literature is also made.Comment: 11 Pages and 4 Table
MOJAVE: Monitoring of Jets in AGN with VLBA Experiments - I. First-Epoch 15 GHz Linear Polarization Images
We present first-epoch, milliarcsecond-scale linear polarization images at 15
GHz of 133 jets associated with AGN in the MOJAVE survey (Monitoring of Jets in
Active Galactic Nuclei with VLBA Experiments). The sample consists of all known
AGN with galactic latitude |b| > 2.5 deg., J2000 declination > -20 deg., and 15
GHz VLBA flux density exceeding 1.5 Jy (2 Jy for sources with declination < 0)
at any epoch during the period 1994-2003. Because of strong selection effects,
the sample primarily consists of blazars with parsec-scale morphologies
consisting of a bright core component at the extreme end of a one-sided jet. At
least one third of the compact cores are completely unresolved on the longest
VLBA baselines, indicating brightness temperatures above 10^{11} K. The
unresolved cores tend to have electric vectors that are aligned with the inner
jet direction, suggesting the presence of a stationary transverse shock near
the base of the jet. Many of the extended jet regions display exceedingly high
fractional polarizations (> 50%) and electric vectors aligned with the jet
ridge line, consistent with optically thin emission from transverse shocks.
Both weak- and strong-lined blazars show a general increase in fractional
polarization with distance down the jet, but BL Lac jets are generally more
polarized and have electric vectors preferentially aligned with the local jet
direction. We show that these differences are intrinsic to the jets, and not
due to sample bias. Distinct features in the jets of gamma-ray loud (EGRET)
blazars are typically twice as luminous as those in non-EGRET blazars, and are
more polarized. These differences can be adequately explained if EGRET blazars
have slightly higher Doppler boosting factors than those not yet detected in
gamma-rays.Comment: 48 pages, 13 figures. Submitted for publication in the Astronomical
Journal. A 5 Mb version of the manuscript with high-resolution figures can be
found at http://www.physics.purdue.edu/astro/MOJAVE/paper1/ms.ps.g
prompt production at the Tevatron and LHC in nonrelativistic QCD
With nonrelativistic QCD factorization, we calculate the
prompt production at hadron colliders at next-to-leading order in .
In addition to the color-singlet contribution, color-octet channels (especially
the P-wave channel) up to are all considered. Aside from direct
production, the feed-down contributions from higher excited S-wave and P-wave
states to production are also included. We use the
potential model estimates as input for color-singlet long-distance matrix
elements (LDMEs). While for color-octet contributions, we find they can be
approximately described by three LDMEs: \mo{}{3}{S}{1}{8},
\mo{}{1}{S}{0}{8} and \mo{}{3}{P}{0}{8}. By fitting the Tevatron data we
can determine some linear combinations of these LDMEs, and then use them to
predict production at the LHC. Our predictions are consistent
with the new experimental data of CMS and LHCb.Comment: Version published in PRD, references added, 15 pages, 3 figure
Effects of Foreground Contamination on the Cosmic Microwave Background Anisotropy Measured by MAP
We study the effects of diffuse Galactic, far-infrared extragalactic source,
and radio point source emission on the cosmic microwave background (CMB)
anisotropy data anticipated from the MAP experiment. We focus on the
correlation function and genus statistics measured from mock MAP
foreground-contaminated CMB anisotropy maps generated in a spatially-flat
cosmological constant dominated cosmological model. Analyses of the simulated
MAP data at 90 GHz (0.3 deg FWHM resolution smoothed) show that foreground
effects on the correlation function are small compared with cosmic variance.
However, the Galactic emission, even just from the region with |b| > 20 deg,
significantly affects the topology of CMB anisotropy, causing a negative genus
shift non-Gaussianity signal. Given the expected level of cosmic variance, this
effect can be effectively reduced by subtracting existing Galactic foreground
emission models from the observed data. IRAS and DIRBE far-infrared
extragalactic sources have little effect on the CMB anisotropy. Radio point
sources raise the amplitude of the correlation function considerably on scales
below 0.5 deg. Removal of bright radio sources above a 5 \sigma detection limit
effectively eliminates this effect. Radio sources also result in a positive
genus curve asymmetry (significant at 2 \sigma) on 0.5 deg scales. Accurate
radio point source data is essential for an unambiguous detection of CMB
anisotropy non-Gaussianity on these scales. Non-Gaussianity of cosmological
origin can be detected from the foreground-subtracted CMB anisotropy map at the
2 \sigma level if the measured genus shift parameter |\Delta\nu| >= 0.02 (0.04)
or if the measured genus asymmetry parameter |\Delta g| >= 0.03 (0.08) on a 0.3
(1.0) deg FWHM scale.Comment: 26 pages, 7 figures, Accepted for Publication in Astrophysical
Journal (Some sentences and figures modified
Galactic microwave emission at degree angular scales
We cross-correlate the Saskatoon Ka and Q-Band Cosmic Microwave Background
(CMB) data with different maps to quantify possible foreground contamination.
We detect a marginal correlation (2 sigma) with the Diffuse Infrared Background
Experiment (DIRBE) 240, 140 and 100 microm maps, but we find no significant
correlation with point sources, with the Haslam 408 MHz map or with the Reich
and Reich 1420 MHz map. The rms amplitude of the component correlated with
DIRBE is about 20% of the CMB signal. Interpreting this component as free-free
emission, this normalization agrees with that of Kogut et al. (1996a; 1996b)
and supports the hypothesis that the spatial correlation between dust and warm
ionized gas observed on large angular scales persists to smaller angular
scales. Subtracting this contribution from the CMB data reduces the
normalization of the Saskatoon power spectrum by only a few percent.Comment: Minor revisions to match published version. 14 pages, with 2 figures
included. Color figure and links at
http://www.sns.ias.edu/~angelica/foreground.htm
A Nanofiber-Based Optical Conveyor Belt for Cold Atoms
We demonstrate optical transport of cold cesium atoms over millimeter-scale
distances along an optical nanofiber. The atoms are trapped in a
one-dimensional optical lattice formed by a two-color evanescent field
surrounding the nanofiber, far red- and blue-detuned with respect to the atomic
transition. The blue-detuned field is a propagating nanofiber-guided mode while
the red-detuned field is a standing-wave mode which leads to the periodic axial
confinement of the atoms. Here, this standing wave is used for transporting the
atoms along the nanofiber by mutually detuning the two counter-propagating
fields which form the standing wave. The performance and limitations of the
nanofiber-based transport are evaluated and possible applications are
discussed
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