271 research outputs found
The First Moments of Nucleon Generalized Parton Distributions
We extrapolate the first moments of the generalized parton distributions
using heavy baryon chiral perturbation theory. The calculation is based on the
one loop level with the finite range regularization. The description of the
lattice data is satisfactory and the extrapolated moments at physical pion mass
are consistent with the results obtained with dimensional regularization,
although the extrapolation in the momentum transfer to does show
sensitivity to form factor effects which lie outside the realm of chiral
perturbation theory. We discuss the significance of the results in the light of
modern experiments as well as QCD inspired models.Comment: 14 pages, 9 figure
Simulations of a Scintillator Compton Gamma Imager for Safety and Security
We are designing an all-scintillator Compton gamma imager for use in security
investigations and remediation actions involving radioactive threat material.
To satisfy requirements for a rugged and portable instrument, we have chosen
solid scintillator for the active volumes of both the scatter and absorber
detectors. Using the BEAMnrc/EGSnrc Monte Carlo simulation package, we have
constructed models using four different materials for the scatter detector:
LaBr_3, NaI, CaF_2 and PVT. We have compared the detector performances using
angular resolution, efficiency, and image resolution. We find that while PVT
provides worse performance than that of the detectors based entirely on
inorganic scintillators, all of the materials investigated for the scatter
detector have the potential to provide performance adequate for our purposes.Comment: Revised text and figures, Presented at SORMA West 2008, Published in
IEEE Transactions on Nuclear Scienc
Double deeply virtual Compton scattering off the nucleon
We study the double deeply virtual Compton scattering (DDVCS) process off the
nucleon, through the scattering of a spacelike virtual photon with large
virtuality resulting in the production of a timelike virtual photon, decaying
into an e^+ e^- pair. This process is expressed in the Bjorken regime in terms
of generalized parton distributions (GPDs) and it is shown that by varying the
invariant mass of the lepton pair, one can directly extract the GPDs from the
observables. We give predictions for the DDVCS cross section and beam helicity
asymmetry and discuss its experimental feasibility.Comment: 4 pages, 4 figure
The DVCS Measurement at HERA
The recent results of the studies of Deeply Virtual Compton Scattering (DVCS)
events at HERA are presented. The possibility offered by this process to gain
information about skewed parton distributions (SPD) is emphasized.Comment: Talk given at New Trends in HERA Physics 2001, Ringberg Castle,
Tegernsee, Germany, 17-22 Jun 2001, 13 pages, 10 figures, recent ZEUS data
discussed, references update
Review of tau lifetime measurements
The measurements of the mean lifetime of the tau lepton are reviewed. The
conditions for measuring the lifetime at various e+e- colliders are compared
and the analysis methods are briefly described. The new developments since the
previous Workshop on Tau Lepton Physics are listed. The world average is
tau_tau = 290.5 +- 1.0 fs. The LEP experiments dominate this average and have
analyzed nearly all of their data. In anticipation of the next era of precision
measurements at CLEO and the b factories, the important sources of systematic
errors and the treatment of systematic biases are discussed.Comment: Invited talk presented at the Fifth International Workshop on Tau
Lepton Physics, Santander, Spain, 14-17 September 1998; 10 pages, 8 figure
Aerial Measurement of Radioxenon Concentration off the West Coast of Vancouver Island following the Fukushima Reactor Accident
In response to the Fukushima nuclear reactor accident, on March 20th, 2011,
Natural Resources Canada conducted aerial radiation surveys over water just off
of the west coast of Vancouver Island. Dose-rate levels were found to be
consistent with background radiation, however a clear signal due to Xe-133 was
observed. Methods to extract Xe-133 count rates from the measured spectra, and
to determine the corresponding Xe-133 volumetric concentration, were developed.
The measurements indicate that Xe-133 concentrations on average lie in the
range of 30 to 70 Bq/m3.Comment: 14 pages, 5 figures, accepted for publication in Journal of
Environmental Radioactivit
Determination of the Michel Parameters rho, xi, and delta in tau-Lepton Decays with tau --> rho nu Tags
Using the ARGUS detector at the storage ring DORIS II, we have
measured the Michel parameters , , and for
decays in -pair events produced at
center of mass energies in the region of the resonances. Using
as spin analyzing tags, we find , , , , and . In addition, we report
the combined ARGUS results on , , and using this work
und previous measurements.Comment: 10 pages, well formatted postscript can be found at
http://pktw06.phy.tu-dresden.de/iktp/pub/desy97-194.p
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