1,096 research outputs found
Three-body analysis of incoherent -photoproduction on the deuteron in the near threshold region
A three-body calculation of the reaction in the energy
region from threshold up to 30 MeV above has been performed. The primary goal
of this study is to assess the importance of the three-body aspects in the
hadronic sector of this reaction. Results are presented for the -meson
spectrum as well as for the total cross section. The three-body results differ
significantly from those predicted by a simple rescattering model in which only
first-order - and -interactions in the final state are considered.
The major features of the experimental data are well reproduced although right
at threshold the rather large total cross section could not be explained.Comment: 6 pages revtex including 3 figure
The new low frequency accelerating systems for the CERN PS booster
A set of four, ferrite-loaded, low-frequency RF cavities equipped with local RF feedback has been built and installed in the CERN PS Booster rings. Together with the modified existing RF systems they now serve for acceleration as well as RF gymnastics of protons and heavy ions up to the highest beam intensities. The systems specifications with a frequency range of about 0.6 to 1.8 MHz and a nomina l RF peak voltage of 8 kV satisfy specifically the requirements of acceleration on harmonic 1 of the future proton beam for the LHC. The system design has been guided by the request for safety margins for high beam intensity operation and ease of maintenance and repair. Some design aspects are presented as well as the performance achieved
Photoproduction of mesons off neutrons from a deuteron target
A formalism is developed for the partial wave analysis of data on meson
photoproduction off deuterons and applied to photoproduction of and
mesons. Different interpretations of a dip-bump structure of the
photoproduction cross section in the 1670 MeV region are presented and
discussed. Helicity amplitudes for two low-mass states are determined.Comment: 11 pages, 13 figure
Interference phenomena in the -wave in photoproduction
The recent precise experimental results for the photoproduction of
-mesons off the neutron measured with the Crystal Ball/TAPS calorimeter
at the MAMI accelerator have been investigated in detail in the framework of
the Bonn-Gatchina coupled channel model. The main result is that the narrow
structure observed in the excitation function of
can be reproduced fully with a particular interference pattern in the
partial wave. Introduction of the narrow resonance with
the properties reported in earlier publications deteriorates the quality of the
fit.Comment: 10 pages, 13 figures, accepted for publication in EPJ
Coherent -photoproduction on He and C in the near-threshold region
Coherent meson photoproduction on He and C is considered in
the near-threshold region. The elementary photoproduction operator
includes contributions from the and resonances as
well as -channel vector meson exchange and the nucleon pole terms. Due to
the suppression of the dominant resonance for spin and isospin
saturated nuclei, the reaction is mainly governed by exchange.
Furthermore, the influence of Fermi motion and of different prescriptions for
the choice of the invariant reaction energy in the elementary
amplitude is studied.Comment: 27 pages revtex including 9 postscript figure
Photoproduction of pions and etas in nuclei
We calculate the cross sections for inclusive one-pion, two-pion and eta
photoproduction in nuclei in the photon energy range from 300 MeV to 900 MeV
within the framework of a semi-classical BUU transport model. Our results are
compared with existing experimental data and discussed with respect to a
calculation of the total photoabsorption cross section.Comment: 30 pages LaTeX including 13 postscript figure
Adaptive planning in human search
How do people plan ahead when searching for rewards? We
investigate planning in a foraging task in which participants
search for rewards on an infinite two-dimensional grid. Our
results show that their search is best-described by a model
which searches at least 3 steps ahead. Furthermore, participants do not seem to update their beliefs during planning, but
rather treat their initial beliefs as given, a strategy similar to a
heuristic called root-sampling. This planning algorithm corresponds well with participantsâ behavior in test problems with
restricted movement and varying degrees of information, outperforming more complex models. These results enrich our
understanding of adaptive planning in complex environments
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
Incoherent Eta Photoproduction from the Deuteron near Threshold
Very recent data for the reaction gamma+d ->eta np, namely total cross
sections, angular and momentum spectra, are analyzed within a model that
includes contributions from the impulse approximation and next order
corrections due to the np and eta-N interactions in the final state. Comparison
between the calculations and the new data indicate sizable contributions from
the np and eta-N final state interactions. Some systematic discrepancies
between the calculations and the data are also found
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