Data on the polarization observables T, P, and H for the reaction γp→pπ0 are reported. Compared to earlier data from other experiments, our data are more precise and extend the covered range in ...energy and angle substantially. The results were extracted from azimuthal asymmetries measured using a transversely polarized target and linearly polarized photons. The data were taken at the Bonn electron stretcher accelerator ELSA with the CBELSA/TAPS detector. Within the Bonn-Gatchina partial wave analysis, the new polarization data lead to a significant narrowing of the error band for the multipoles for neutral-pion photoproduction.
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.
Polarization measurements of TEMPO-doped butanol targets Plückthun, M.; Bradtke, Ch; Dutz, H. ...
Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment,
11/1997, Letnik:
400, Številka:
1
Journal Article
Recenzirano
Dynamic nuclear polarization (DNP) measurements have been performed in butanol and deuterated butanol. Both target materials have been chemically prepared for the DNP process with the highly stable ...free nitroxyl radical 2,2,6,6-tetramethyl-piperidine-1-oxyl, also known as TEMPO. Maximum proton polarization values of 89.2% and maximum deuteron polarization values of 38.4% have been obtained in a magnetic field of 2.5 T and at a temperature of about 200 mK. Polarization relaxation times of >200 h (protons) and >100 h (deuterons) have been measured at 0.35 T and 60 mK. The results together with an easy preparation procedure make TEMPO-doped butanol attractive for the frozen spin operation mode of polarized solid-state targets.
A measurement of the helicity dependence of the total inclusive photoabsorption cross section on the deuteron was carried out at MAMI (Mainz) in the energy range 200<Eγ<800 MeV. The experiment used a ...4π detection system, a circularly polarized tagged photon beam and a frozen spin target which provided longitudinally polarized deuterons. These new results are a significant improvement on the existing data and allow a detailed comparison with state-of-the-art calculations.
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.
A new concept of a small superconducting ‘holding magnet’, placed inside a polarization refrigerator, has been developed for frozen spin targets. The superconducting wire is wound on the inner ...cooling shield of the vertical dilution refrigerator of the Bonn Frozen Spin Target (BoFroST). The maximum field of the magnet is 0.38
tesla. Based on this concept, the frozen spin target was used for a measurement of the target asymmetry in the η-photoproduction γp↑→ηp with the PHOENICS-detector at the Bonn electron stretcher accelerator ELSA.
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