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.
.
Results from measurements of the photoproduction of
η
mesons from quasifree protons and neutrons are summarized. The experiments were performed with the CBELSA/TAPS detector at the electron ...accelerator ELSA in Bonn using the
η
→
3
π
0
→
6
γ
decay. A liquid deuterium target was used for the measurement of total cross sections and angular distributions. The results confirm earlier measurements from Bonn and the MAMI facility in Mainz about the existence of a narrow structure in the excitation function of
γ
n
→
n
η
. The current angular distributions show a forward-backward asymmetry, which was previously not seen, but was predicted by model calculations including an additional narrow
P
11
state. Furthermore, data obtained with a longitudinally polarized, deuterated butanol target and a circularly polarized photon beam were analyzed to determine the double polarization observable
E
. Both data sets together were also used to extract the helicity-dependent cross sections
σ
1
/
2
and
σ
3
/
2
. The narrow structure in the excitation function of
γ
n
→
n
η
appears associated with the helicity-1/2 component of the reaction.
The first measurements of the beam-target-helicity-asymmetries E and G in the photoproduction of ω-mesons off protons at the CBELSA/TAPS experiment are reported. E (G) was measured using circularly ...(linearly) polarised photons and a longitudinally polarised target. E was measured over the photon energy range from close to threshold (Eγ=1108 MeV) to Eγ=2300 MeV and G at a single energy interval of 1108<Eγ<1300 MeV. Both measurements cover the full solid angle. The observables E and G are highly sensitive to the contribution of baryon resonances, with E acting as a helicity filter in the s-channel. The new results indicate significant s-channel resonance contributions together with contributions from t-channel exchange processes. A partial wave analysis reveals strong contributions from the partial waves with spin-parity JP=3/2+,5/2+, and 3/2−.
.
This paper reports on a measurement of the double-polarization observable
G
in
π
0
photoproduction off the proton using the CBELSA/TAPS experiment at the ELSA accelerator in Bonn. The observable
G
...is determined from reactions of linearly polarized photons with longitudinally polarized protons. The polarized photons are produced by bremsstrahlung off a diamond radiator of well-defined orientation. A frozen spin butanol target provides the polarized protons. The data cover the photon energy range from 617 to 1325 MeV and a wide angular range. The experimental results for
G
are compared to predictions by the Bonn-Gatchina (BnGa), Jülich-Bonn (JüBo), MAID and SAID partial wave analyses. Implications of the new data for the pion photoproduction multipoles are discussed.
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.
Abstract
A measurement of the double-polarization observable
E
for the reaction
$$\gamma p\rightarrow \pi ^0 p$$
γ
p
→
π
0
p
is reported. The data were taken with the CBELSA/TAPS experiment at the ...ELSA facility in Bonn using the Bonn frozen-spin butanol (C
$$_4$$
4
H
$$_9$$
9
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
$$E_\gamma =600$$
E
γ
=
600
to 2310 MeV and nearly the complete angular range. The results are compared to and have been included in recent partial wave analyses.
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.
A measurement of the double-polarization observable
E
for the reaction
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\begin{document}$$\gamma p\rightarrow \pi ^0 p$$\end{document}
γ
p
→
π
0
p
is reported. The data were taken with the CBELSA/TAPS experiment at the ELSA facility in Bonn using the Bonn frozen-spin butanol (C
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\begin{document}$$_4$$\end{document}
4
H
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9
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
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\begin{document}$$E_\gamma =600$$\end{document}
E
γ
=
600
to 2310 MeV and nearly the complete angular range. The results are compared to and have been included in recent partial wave analyses.
A measurement of the double-polarization observable E for the reaction γp→π0p is reported. The data were taken with the CBELSA/TAPS experiment at the ELSA facility in Bonn using the Bonn frozen-spin ...butanol (C4H9OH) 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 Eγ=600 to 2310 MeV and nearly the complete angular range. The results are compared to and have been included in recent partial wave analyses.
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