Photoproduction of two neutral pions off the proton is studied using linearly polarized photons, and the polarization observables Is and Ic are measured for the first time. These two observables are ...unique to multi-meson final states; they characterize correlations between the linear photon polarization and the direction of outgoing single particles in photoproduction of three-body final states. The Is and Ic distributions suggest that, in the 1.8 to 2.0 GeV mass region, the N(1520)3/2−π intermediate state is reached with reaction dynamics consistent with a dominant JP=3/2+ wave. These data are included in the Bonn–Gatchina (BnGa) partial wave analysis which is based on a large variety of data; the analysis confirms a significant contribution from the reaction chain γp→N(1900)3/2+→N(1520)3/2−π0→pπ0π0.
A measurement of the double-polarization observable
for the reaction
is reported. The data were taken with the CBELSA/TAPS experiment at the ELSA facility in Bonn using the Bonn frozen-spin butanol ...(C
H
OH) target, which provided longitudinally-polarized protons. Circularly-polarized photons were produced via bremsstrahlung of longitudinally-polarized electrons. The data cover the photon energy range from
to 2310 MeV and nearly the complete angular range. The results are compared to and have been included in recent partial wave analyses.
The photoproduction of 2
π
0
mesons off protons was studied with the Crystal Barrel/TAPS experiment at the electron accelerator ELSA in Bonn. The energy of photons produced in a radiator was tagged ...in the energy range from 600 MeV to 2.5 GeV. Differential and total cross sections and
pπ
0
π
0
Dalitz plots are presented. Part of the data was taken with a diamond radiator producing linearly polarized photons, and beam asymmetries were derived. Properties of nucleon and
Δ
resonances contributing to the
pπ
0
π
0
final state were determined within the Bonn-Gatchina (BnGa) partial-wave analysis. The data presented here allow us to determine branching ratios of nucleon and
Δ
resonances for their decays into
pπ
0
π
0
via several intermediate states. Most prominent are decays proceeding via
Δ
(1232)
π
,
N
(1440)1/2
+
π
,
N
(1520)3/2
−
π
,
N
(1680)5/2
+
π
, but also
pf
0
(500),
pf
0
(980), and
pf
2
(1270) contribute to the reaction.
Photoproduction off protons of the
pπ
0
η
three-body final state was studied with the Crystal Barrel/TAPS detector, at the electron stretcher accelerator ELSA in Bonn, for incident energies from the
...π
0
η
production threshold up to 2.5 GeV. Differential cross sections and the total cross sections are presented. The use of linearly polarized photons gives access to the polarization observables
Σ
,
I
s
, and
I
c
, the latter two characterize beam asymmetries in case of three-body final states.
Δ
(1232)
η
,
N
(1535)1/2
−
π
, and
pa
0
(980) are the dominant isobars contributing to the reaction. The partial wave analysis confirms the existence of some nucleon and
Δ
resonances, for which so far only fair evidence was reported. A large number of decay modes of known nucleon and
Δ
resonances is presented. It is shown that detailed investigations of decay branching ratios may provide a key to unravelling the structure of nucleon and
Δ
resonances.
The excitation function and momentum distribution of {\eta}' mesons have been measured in photoproduction off 93^Nb in the energy range of 1.2-2.9 GeV. The experiment has been performed with the ...combined Crystal Barrel and MiniTAPS detector system, using tagged photon beams from the ELSA electron accelerator. Information on the sign and magnitude of the real part of the {\eta}'-Nb potential has been extracted from a comparison of the data with model calculations. An attractive potential of -(41 \pm 10(stat) \pm 15(syst)) MeV depth at normal nuclear matter density is deduced within model uncertainties. This value is consistent with the potential depth of -(37 \pm 10(stat) \pm 10(syst)) MeV obtained in an earlier measurement for a light nucleus (carbon). This relatively shallow {\eta}'-nucleus potential will make the search for {\eta}'-nucleus bound states more difficult.
The cover shows a cavity in a metal foam which developed due to large heat effects in the foam during welding. More about joining strategies of open porous metallic foams can be found in the paper by ...S. Angel, W. Bleck et al. on page 670.
Within the Collaborative Research Centre (SFB) 561 “Thermally highly loaded, porous and cooled multilayer systems for combined cycle power plants” open porous Ni‐based structures are developed for the requirements of an effusion cooling. A two‐dimensional cooling strategy for the walls of combustion chambers, that allows the outflow of the cooling medium over the complete wall area of the combustion chamber, could be realized by an open porous metallic foam structure. The challenge is to join the porous foam structure with the solid substrate material. Capacitor discharge welding and laser beam welding/‐brazing methods seems to be promising methods due to a minimum input of energy and, connected with this, a small joining zone.
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