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Review of the SLAC and Les Houches workshops
Polarized Electron Source workshops have been held at varying intervals, beginning in 1983 when Charles Sinclair convened the first at SLAC. Since that time, three workshops were held in conjunction with the International Spin Symposia and two at other occasions. The increasing importance of polarized electron beams at accelerators has stimulated interest in these workshops. Two workshops have been held since the last International Spin Symposium in Nagoya. In 1993, a workshop was held at SLAC, and in 1994 at Les Houches, a polarized electron beam session was held as part of a polarized beam and targets workshop. This report summarizes highlights from the latter two workshops
Measurement of the parity violating 6S-7S transition amplitude in cesium achieved within 2 \times 10^{-13} atomic-unit accuracy by stimulated-emission detection
We exploit the process of asymmetry amplification by stimulated emission
which provides an original method for parity violation (PV) measurements in a
highly forbidden atomic transition. The method involves measurements of a
chiral, transient, optical gain of a cesium vapor on the 7S-6P_{3/2}
transition, probed after it is excited by an intense, linearly polarized,
collinear laser, tuned to resonance for one hyperfine line of the forbidden
6S-7S transition in a longitudinal electric field. We report here a 3.5 fold
increase, of the one-second-measurement sensitivity, and subsequent reduction
by a factor of 3.5 of the statistical accuracy compared with our previous
result [J. Gu\'ena et al., Phys. Rev. Lett. 90, 143001 (2003)]. Decisive
improvements to the set-up include an increased repetition rate, better
extinction of the probe beam at the end of the probe pulse and, for the first
time to our knowledge, the following: a polarization-tilt magnifier,
quasi-suppression of beam reflections at the cell windows, and a Cs cell with
electrically conductive windows. We also present real-time tests of systematic
effects, consistency checks on the data, as well as a 1% accurate measurement
of the electric field seen by the atoms, from atomic signals. PV measurements
performed in seven different vapor cells agree within the statistical error.
Our present result is compatible with the more precise Boulder result within
our present relative statistical accuracy of 2.6%, corresponding to a 2 \times
10^{-13} atomic-unit uncertainty in E_1^{pv}. Theoretical motivations for
further measurements are emphasized and we give a brief overview of a recent
proposal that would allow the uncertainty to be reduced to the 0.1% level by
creating conditions where asymmetry amplification is much greater.Comment: Article 21 pages, 6 figures, 3 tables Typos, addition of few comments
and little more data (1 week) leading to a slight reduction of the error bar
Accepted for publication in Phys.Rev.
Atomic Hydrogen Cleaning of Polarized GaAs Photocathodes
Atomic hydrogen cleaning followed by heat cleaning at 450C was used
to prepare negative-electron-affinity GaAs photocathodes. When hydrogen ions
were eliminated, quantum efficiencies of 15% were obtained for bulk GaAs
cathodes, higher than the results obtained using conventional 600C heat
cleaning. The low-temperature cleaning technique was successfully applied to
thin, strained GaAs cathodes used for producing highly polarized electrons. No
depolarization was observed even when the optimum cleaning time of about 30
seconds was extended by a factor of 100
Central Powering of the Largest Lyman-alpha Nebula is Revealed by Polarized Radiation
High-redshift Lyman-alpha blobs are extended, luminous, but rare structures
that appear to be associated with the highest peaks in the matter density of
the Universe. Their energy output and morphology are similar to powerful radio
galaxies, but the source of the luminosity is unclear. Some blobs are
associated with ultraviolet or infrared bright galaxies, suggesting an extreme
starburst event or accretion onto a central black hole. Another possibility is
gas that is shock excited by supernovae. However some blobs are not associated
with galaxies, and may instead be heated by gas falling into a dark matter
halo. The polarization of the Ly-alpha emission can in principle distinguish
between these options, but a previous attempt to detect this signature returned
a null detection. Here we report on the detection of polarized Ly-alpha from
the blob LAB1. Although the central region shows no measurable polarization,
the polarized fraction (P) increases to ~20 per cent at a radius of 45 kpc,
forming an almost complete polarized ring. The detection of polarized radiation
is inconsistent with the in situ production of Ly-alpha photons, and we
conclude that they must have been produced in the galaxies hosted within the
nebula, and re-scattered by neutral hydrogen.Comment: Published in the August 18 issue of Nature. 1750 words, 3 figures,
and full Supplementary Information. Version has not undergone proofing.
Reduced and processed data products are available here:
http://obswww.unige.ch/people/matthew.hayes/LymanAlpha/LabPol
Wide Area Network Access to CMS Data Using the Lustre Filesystem
In this paper, we explore the use of the Lustre cluster filesystem over the wide area network to access Compact Muon Solenoid (CMS) data stored on physical devices located hundreds of kilometres away. We describe the experimental testbed and report on the I/O performance of applications writing and reading data on the distributed Lustre filesystem established across the WAN. We compare the I/O performance of a CMS application to the performance obtained with IOzone, a standard benchmark tool. We then examine the I/O performance of the CMS application running multiple processes on a single server. And compare the Lustre results to results obtained on data stored on local filesystems. Our measurements reveal that the IOzone benchmark tool, accessing data sequentially, can saturate the Gbps network link that connects our Lustre client in Miami Florida to the Lustre storage located in Gainesville, Florida. We also find that the I/O rates of the CMS application is significantly less than what can be obtained with IOzone for sequential access to data
SU(3) assignment and coupling of N*(1688)
A comparison of the two reactions Îł + p â n + p and Îł + p â Ï0 + p in the region of the third nucleon isobar N***(1688) has produced evidence that (1) N***(1688) is a member of a unitary octet, and (2) the D/F ratio, which relates the couplings N***N Ï and N***Nn, is similar to that which relates NN Ï and NNn
The Intrinsically X-ray Weak Quasar PHL 1811. I. X-ray Observations and Spectral Energy Distribution
This is the first of two papers reporting observations and analysis of the
unusually bright (m_b=14.4), luminous (M_B=-25.5), nearby (z=0.192) narrow-line
quasar PHL 1811, focusing on the X-ray properties and the spectral energy
distribution. Two Chandra observations reveal a weak X-ray source with a steep
spectrum. Variability by a factor of 4 between the two observations separated
by 12 days suggest that the X-rays are not scattered emission. The XMM-Newton
spectra are modelled in the 0.3--5 keV band by a steep power law with \Gamma =
2.3\pm 0.1, and the upper limit on intrinsic absorption is 8.7 x 10^{20}
cm^{-2}. The spectral slopes are consistent with power law indices commonly
observed in NLS1s, and it appears that we observe the central engine X-rays
directly. Including two recent Swift ToO snapshots, a factor of ~5 variability
was observed among the five X-ray observations reported here. In contrast, the
UV photometry obtained by the XMM-Newton OM and Swift UVOT, and the HST
spectrum reveal no significant UV variability. The \alpha_{ox} inferred from
the Chandra and contemporaneous HST spectrum is -2.3 \pm 0.1, significantly
steeper than observed from other quasars of the same optical luminosity. The
steep, canonical X-ray spectra, lack of absorption, and significant X-ray
variability lead us to conclude that PHL 1811 is intrinsically X-ray weak. We
also discuss an accretion disk model, and the host galaxy of PHL 1811.Comment: 45 pages, 9 figures, accepted for publication in Ap
Gas Accretion and Giant Lyman-alpha Nebulae
Several decades of observations and discoveries have shown that high-redshift
AGN and massive galaxies are often surrounded by giant Lyman-alpha nebulae
extending in some cases up to 500 kpc in size. In this review, I discuss the
properties of the such nebulae discovered at z>2 and their connection with gas
flows in and around the galaxies and their halos. In particular, I show how
current observations are used to constrain the physical properties and origin
of the emitting gas in terms of the Lyman-alpha photon production processes and
kinematical signatures. These studies suggest that recombination radiation is
the most viable scenario to explain the observed Lyman-alpha luminosities and
Surface Brightness for the large majority of the nebulae and imply that a
significant amount of dense, ionized and cold clumps should be present within
and around the halos of massive galaxies. Spectroscopic studies suggest that,
among the giant Lyman-alpha nebulae, the one associated with radio-loud AGN
should have kinematics dominated by strong, ionized outflows within at least
the inner 30-50 kpc. Radio-quiet nebulae instead present more quiescent
kinematics compatible with stationary situation and, in some cases, suggestive
of rotating structures. However, definitive evidences for accretion onto
galaxies of the gas associated with the giant Lyman-alpha emission are not
unambiguously detected yet. Deep surveys currently ongoing using other bright,
non-resonant lines such as Hydrogen H-alpha and HeII1640 will be crucial to
search for clearer signatures of cosmological gas accretion onto galaxies and
AGN.Comment: Invited review to appear in Gas Accretion onto Galaxies, Astrophysics
and Space Science Library, eds. A. J. Fox & R. Dave', to be published by
Springe
Observation of single collisionally cooled trapped ions in a buffer gas
Individual Ba ions are trapped in a gas-filled linear ion trap and observed
with a high signal-to-noise ratio by resonance fluorescence. Single-ion storage
times of ~5 min (~1 min) are achieved using He (Ar) as a buffer gas at
pressures in the range 8e-5 - 4e-3 torr. Trap dynamics in buffer gases are
experimentally studied in the simple case of single ions. In particular, the
cooling effects of light gases such as He and Ar and the destabilizing
properties of heavier gases such as Xe are studied. A simple model is offered
to explain the observed phenomenology.Comment: 5 pages, 4 figures, accepted for publication in Phys. Rev. A. Minor
text and figure change
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