290 research outputs found
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
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.
K0-Sigma+ Photoproduction with SAPHIR
Preliminary results of the analysis of the reaction p(gamma,K0)Sigma+ are
presented. We show the first measurement of the differential cross section and
much improved data for the total cross section than previous data. The data are
compared with model predictions from different isobar and quark models that
give a good description of p(gamma,K+)Lambda and p(gamma,K+)Sigma0 data in the
same energy range. Results of ChPT describe the data adequately at threshold
while isobar models that include hadronic form factors reproduce the data at
intermediate energies.Comment: 4 pages, Latex2e, 4 postscript figures. Talk given at the
International Conference on Hypernuclear and Strange Particle Physics
(HYP97), Brookhaven National Laboratory, USA, October 13-18, 1997. To be
published in Nucl. Phys. A. Revised version due to changes in experimental
dat
Evidence for the positive-strangeness pentaquark in photoproduction with the SAPHIR detector at ELSA
The positive--strangeness baryon resonance is observed in
photoproduction of the final state with the SAPHIR detector at
the Bonn ELectron Stretcher Accelerator ELSA. It is seen as a peak in the invariant mass distribution with a confidence level. We find
a mass MeV and an upper limit of the width
MeV at 90% c.l. From the absence of a signal in
the invariant mass distribution in at the
expected strength we conclude that the must be isoscalar.Comment: 9 pages, 4 figure
On the benchmarking of multi-junction photoelectrochemical fuel generating devices
We discuss benchmarking considerations for multi-junction solar fuel absorbers and investigate the effects of spectral shaping by catalyst nanoparticles on design criteria.MMM acknowledges funding from the fellowship programme of the German National Academy of Sciences Leopoldina, grant LPDS 2015-09
Photoproduction of {\omega} Mesons off the Proton
The differential cross sections and unpolarized spin-density matrix elements
for the reaction were measured using the CBELSA/TAPS
experiment for initial photon energies ranging from the reaction threshold to
2.5 GeV. These observables were measured from the radiative decay of the
meson, . The cross sections cover the full
angular range and show the full extent of the -channel forward rise. The
overall shape of the angular distributions in the differential cross sections
and unpolarized spin-density matrix elements are in fair agreement with
previous data. In addition, for the first time, a beam of linearly-polarized
tagged photons in the energy range from 1150 MeV to 1650 MeV was used to
extract polarized spin-density matrix elements.
These data were included in the Bonn-Gatchina partial wave analysis (PWA).
The dominant contribution to photoproduction near threshold was found
to be the partial wave, which is primarily due to the sub-threshold
resonance. At higher energies, pomeron-exchange was found to
dominate whereas -exchange remained small. These -channel contributions
as well as further contributions from nucleon resonances were necessary to
describe the entire dataset: the , , and partial waves
were also found to contribute significantly.Comment: 8 pages, 5 figures, accepted for publication in Physics Letters
Measurement of polarisation observables in photoproduction off the proton
The reaction is studied in the
photon energy range from threshold. Linearly polarised photon beams from
coherent bremsstrahlung enabled the first measurement of photon beam
asymmetries in this reaction up to MeV. In addition, the
recoil hyperon polarisation was determined through the asymmetry in the weak
decay up to MeV. The data are
compared to partial wave analyses, and the possible impact on the
interpretation of a recently observed cusp-like structure near the
thresholds is discussed.Comment: 6 pages, 5 figures. References [8,9,10,11] which were not on the
original submission are now include
Experimental constraints on the -nucleus real potential
In a search for mesic states, the production of -mesons in
coincidence with forward going protons has been studied in photon induced
reactions on C for incident photon energies of 1250 - 3100 MeV. The
pairs from decays of bound or quasi-free -mesons have
been measured with the CBELSA/TAPS detector system in coincidence with protons
registered in the MiniTAPS forward array. Structures in the total energy
distribution of the pairs, which would indicate the population
and decay of bound B states, are not observed. The
cross section of 0.3 nb/MeV/sr observed in the bound state energy regime
between -100 and 0 MeV may be accounted for by yield leaking into the bound
state regime because of the large in-medium width of the -meson. A
comparison of the measured total energy distribution with calculations suggests
the real part of the B potential to be small and only
weakly attractive with 35(stat) 20(syst) MeV
in contrast to some theoretical predictions of attractive potentials with a
depth of 100 - 150 MeV.Comment: 13 pages, 8 figure
First measurement of the helicity asymmetry for in the resonance region
The first measurement of the helicity dependence of the photoproduction cross
section of single neutral pions off protons is reported for photon energies
from 600 to 2300\,MeV, covering nearly the full solid angle. The data are
compared to predictions from the SAID, MAID, and BnGa partial wave analyses.
Strikingly large differences between data and predictions are observed which
are traced to differences in the helicity amplitudes of well known and
established resonances. Precise values for the helicity amplitudes of several
resonances are reported
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