617 research outputs found
On the Extraction of Cross Sections for pi0 and eta Photoproduction off Neutrons from Deuteron Data
We discuss the procedure of extracting the photoproduction cross section for
neutral pseudoscalar mesons off neutrons from deuteron data. The main statement
is that the final-state interaction (FSI) corrections for the proton and
neutron target are in general not equal, but for pi0 production there are
special cases were they have to be identical and there are large regions in the
parameter space of incident photon energy and pion polar angle, \theta^*, where
they happen to be quite similar. The corrections for both target nucleons are
practically identical for production in the energy range of the
Delta(1232)3/2+ resonance due to the specific isospin structure of this
excitation. Also above the -isobar range large differences between
proton and neutron correction factors are only predicted for extreme forward
angles ( < 20 deg), but the results are similar for larger angles.
Numerical results for the gp-->pi0p and gn-->pi0n correction factors are
discussed. Also the model description for the available data on the
differential gd-->pi0pn cross sections are given.Comment: 16 pages, 5 figures; v2 fixed several minor typo
Precision high voltage divider for the KATRIN experiment
The Karlsruhe Tritium Neutrino Experiment (KATRIN) aims to determine the
absolute mass of the electron antineutrino from a precise measurement of the
tritium beta-spectrum near its endpoint at 18.6 keV with a sensitivity of 0.2
eV. KATRIN uses an electrostatic retardation spectrometer of MAC-E filter type
for which it is crucial to monitor high voltages of up to 35 kV with a
precision and long-term stability at the ppm level. Since devices capable of
this precision are not commercially available, a new high voltage divider for
direct voltages of up to 35 kV has been designed, following the new concept of
the standard divider for direct voltages of up to 100 kV developed at the
Physikalisch-Technische Bundesanstalt (PTB). The electrical and mechanical
design of the divider, the screening procedure for the selection of the
precision resistors, and the results of the investigation and calibration at
PTB are reported here. During the latter, uncertainties at the low ppm level
have been deduced for the new divider, thus qualifying it for the precision
measurements of the KATRIN experiment.Comment: 22 pages, 12 figure
Crossover from phase fluctuation to amplitude-dominated superconductivity: A model system
We have experimentally studied a model system that demonstrates the crossover from a superconductor that is dominated by phase fluctuations, to one in which the amplitude of the order parameter is the controlling influence on Tc. This model system is comprised of two-dimensional granular Pb with an overlayer of Ag. The system displays many aspects of the phase diagram of the concentration dependence of Tc in the high-Tc superconductors, and this crossover has been applied to explain the phase diagram in that case. We point out the similarities and differences between the model system presented in this paper and the high-Tc superconductors
Measurement of the reaction \gamma p \TO K^ + \Lambda(1520) at photon energies up to 2.65 GeV
The reaction \gamma p \TO K^+\Lambda(1520) was measured in the energy range
from threshold to 2.65 GeV with the SAPHIR detector at the electron stretcher
facility ELSA in Bonn. The production cross section was
analyzed in the decay modes , , , and
as a function of the photon energy and the squared
four-momentum transfer . While the cross sections for the inclusive
reactions rise steadily with energy, the cross section of the process \gamma p
\TO K^+\Lambda(1520) peaks at a photon energy of about 2.0 GeV, falls off
exponentially with , and shows a slope flattening with increasing photon
energy. The angular distributions in the -channel helicity system indicate
neither a nor a exchange dominance. The interpretation of the
as a molecule is not supported.Comment: 11 pages, 16 figures, 4 table
Light Meson Dynamics Workshop. Mini proceedings
The mini-proceedings of the Light Meson Dynamics Workshop held in Mainz from
February 10th to 12th, 2014, are presented. The web page of the conference,
which contains all talks, can be found at
https://indico.cern.ch/event/287442/overview .Comment: 46 pages, 17 contributions. Editors: W. Gradl, P. Masjuan, M.
Ostrick, and S. Schere
The Impact of New Polarization Data from Bonn, Mainz and Jefferson Laboratory on Multipoles
New data on pion-photoproduction off the proton have been included in the
partial wave analyses Bonn-Gatchina and SAID and in the dynamical
coupled-channel approach J\"ulich-Bonn. All reproduce the recent new data well:
the double polarization data for E, G, H, P and T in
from ELSA, the beam asymmetry for and
from Jefferson Laboratory, and the precise new differential cross section and
beam asymmetry data for from MAMI. The new fit
results for the multipoles are compared with predictions not taking into
account the new data. The mutual agreement is improved considerably but still
far from being perfect
Measurement of gamma p --> K+ Lambda and gamma p --> K+ Sigma0 at photon energies up to 2.6 GeV
The reactions gamma p --> K+ Lambda and gamma p --> K+ Sigma0 were measured
in the energy range from threshold up to a photon energy of 2.6 GeV. The data
were taken with the SAPHIR detector at the electron stretcher facility, ELSA.
Results on cross sections and hyperon polarizations are presented as a function
of kaon production angle and photon energy. The total cross section for Lambda
production rises steeply with energy close to threshold, whereas the Sigma0
cross section rises slowly to a maximum at about E_gamma = 1.45 GeV. Cross
sections together with their angular decompositions into Legendre polynomials
suggest contributions from resonance production for both reactions. In general,
the induced polarization of Lambda has negative values in the kaon forward
direction and positive values in the backward direction. The magnitude varies
with energy. The polarization of Sigma0 follows a similar angular and energy
dependence as that of Lambda, but with opposite sign.Comment: 21 pages, 25 figures, submitted to Eur. Phys. J.
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