The polarization observables T,E,P,H, and G in photoproduction of η mesons off protons are measured for photon energies from threshold to W=2400 MeV (T), 2280 MeV (E), 1620 MeV (P,H), or 1820 MeV ...(G), covering nearly the full solid angle. The data are compared to predictions from the SAID, MAID, JüBo, and BnGa partial-wave analyses. A refit within the BnGa approach including further data yields precise branching ratios for the Nη decay of nucleon resonances. A Nη-branching ratio of 0.33±0.04 for N(1650)1/2− is found, which reduces the large and controversially discussed Nη-branching ratio difference of the two lowest mass JP=1/2−-resonances significantly.
The electron spin-lattice relaxation time (T 1 e) of TEMPO- and trityl-doped butanol samples at 2.5 T and temperatures between 0.95 K and 2.17 K was studied by pulsed nuclear magnetic resonance (NMR) ...using the nuclear-electron double resonance (NEDOR) method. This method is based on the idea to measure the NMR lineshift produced by the local field of paramagnetic impurities, whose polarization can be manipulated. This is of technical advantage as measurements can be performed under conditions typically used for the dynamic nuclear polarization (DNP) process - in our case 2.5 T and temperatures around 1 K - where a direct measurement on the electronic spins would be far more complicated to perform.
Deuterated polystyrene for polarized solid targets has been prepared by chemical doping with the trityl radical ‘Finland D36’ (AH 110 355 deutero acid form). Thin foils doped with various radical ...densities have been produced using tetrahydrofuran as solvent. Dynamic nuclear polarization technique has been applied to polarize deuterons in the samples (98%-D) at the temperature range of about 1K and magnetic fields of 2.5T and 5.0T. A maximum deuteron polarization of −61.5% with a build-up time of 100min has been achieved at 5.0T and about 500mK at a radical density of 1.16×1019spins/g.
•Deuterated polystyrene has been prepared by chemical doping with the trityl radical.•Thin foils doped with various radical densities have been produced.•Deuterons are polarized in the samples (98%-D) at about 1K and 2.5T and 5.0T.•Maximum D-polarization of −61.5% with a Tbu of 100min has been achieved.
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.
Chemically doping with trityl radicals was performed in fully deuterated polyethylene. The behavior of paramagnetic centers has been investigated by ESR X-band spectrometer. The highest deuteron ...polarization was 8% at 2.5 T and 1 K with a spin concentration of
3
×
1
0
1
9
spins/g.
The electron spin-lattice relaxation time (T1e) of TEMPO- and trityl-doped butanol samples at 2.5T and temperatures between 0.95K and 2.17K was studied by pulsed nuclear magnetic resonance (NMR) ...using the nuclear-electron double resonance (NEDOR) method. This method is based on the idea to measure the NMR lineshift produced by the local field of paramagnetic impurities, whose polarization can be manipulated. This is of technical advantage as measurements can be performed under conditions typically used for the dynamic nuclear polarization (DNP) process – in our case 2.5T and temperatures around 1K – where a direct measurement on the electronic spins would be far more complicated to perform.
As T1e is a crucial parameter determining the overall efficiency of DNP, the effect of the radical type, its spin concentration, the temperature and the oxygen content on T1e has been investigated.
For radical concentrations as used in DNP (several 1019spins/cm3) the relaxation rate (T1e−1) has shown a linear dependence on the paramagnetic electron concentration for both radicals investigated. Experiments with perdeuterated and ordinary butanol have given no indication for any influence of the host materials isotopes. The measured temperature dependence has shown an exponential characteristic. It is further observed that the oxygen content in the butanol samples has a considerable effect on the electron relaxation time and thus influences the nuclear relaxation time and polarization rate during the DNP.
The experiments also show a variation in the NMR linewidth, leading to comparable time constants as determined by the lineshift. NEDOR measurements were also performed on irradiated, crystal grains of 6LiD. These samples exhibited a linewidth behavior similar to that of the cylindrically shaped butanol samples.
Measurements of target asymmetries and double-polarization observables for the reaction \(\gamma p\to p\pi^0\pi^0\) are reported. The data were taken with the CBELSA/TAPS experiment at the ELSA ...facility (Bonn University) using the Bonn frozen-spin butanol (C\(_4\)H\(_9\)OH) target, which provided transversely polarized protons. Linearly polarized photons were produced via bremsstrahlung off a diamond crystal. The data cover the photon energy range from \(E_{\gamma}\)=650 MeV to \(E_{\gamma}\)=2600 MeV and nearly the complete angular range. The results have been included in the BnGa partial wave analysis. Experimental results and the fit agree very well. Observed systematic differences in the branching ratios for decays of \(N^*\) and \(\Delta^*\) resonances are attributed to the internal structure of these excited nucleon states. Resonances which can be assigned to SU(6)\(\times\)O(3) two-oscillator configurations show larger branching ratios to intermediate states with non-zero intrinsic orbital angular momenta than resonances assigned to one-oscillator configurations.
PDF
