GAMMA P --> ETA P
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Quasi-free photoproduction of eta-mesons of the neutron

The CBELSA & TAPS collaborations Jaegle, I. ; Mertens, T. ; Anisovich, A.V. ; et al.
Phys.Rev.Lett. 100 (2008) 252002, 2008.
Inspire Record 784698 DOI 10.17182/hepdata.50884

Quasi-free photoproduction of eta-mesons off nucleons bound in the deuteron has been measured with the CBELSA/TAPS detector for incident photon energies up to 2.5 GeV at the Bonn ELSA accelerator. The eta-mesons have been detected in coincidence with recoil protons and recoil neutrons, which allows a detailed comparison of the quasi-free n(gamma,eta)n and p(gamma,eta)p reactions. The excitation function for eta-production off the neutron shows a pronounced bump-like structure at W=1.68 GeV (E_g ~ 1 GeV), which is absent for the proton.

22 data tables
Table 1

Measured value of the quasi-free eta cross section off protons and neutrons as a function of incident photon energy.

Table 2

Ratio of the measured quasi-free neutron to proton cross sections as a function of incident photon energy.

Table 3

Measured angular distribution for an incident photon energy of 0.700 GeV.

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Measurement of eta photoproduction on the proton from threshold to 1500-MeV

The GRAAL collaboration Bartalini, O. ; Bellini, V. ; Bocquet, J.P. ; et al.
Eur.Phys.J.A 33 (2007) 169-184, 2007.
Inspire Record 755415 DOI 10.17182/hepdata.51526

Beam asymmetry and differential cross section for the reaction gamma+p->eta+p were measured from production threshold to 1500 MeV photon laboratory energy. The two dominant neutral decay modes of the eta meson, eta->2g and eta->3pi0, were analyzed. The full set of measurements is in good agreement with previously published results. Our data were compared with three models. They all fit satisfactorily the results but their respective resonance contributions are quite different. The possible photoexcitation of a narrow state N(1670) was investigated and no evidence was found.

45 data tables
Table 1

Measured beam asymmetry at photon energy 724 MeV as a function of the ETA centre of mass angle.

Table 2

Measured beam asymmetry at photon energy 761 MeV as a function of the ETA centre of mass angle.

Table 3

Measured beam asymmetry at photon energy 810 MeV as a function of the ETA centre of mass angle.

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Evidence for a narrow structure at W approx. 1.68-GeV in eta photoproduction on the neutron.

The GRAAL collaboration Kuznetsov, Viacheslav ; Churikova, S. ; Gervino, G. ; et al.
Phys.Lett.B 647 (2007) 23-29, 2007.
Inspire Record 720508 DOI 10.17182/hepdata.26995

New results on quasi-free $\eta$ photoproduction on the neutron and proton bound in a deuteron target are presented. The $\gamma n \to \eta n$ quasi-free cross section reveals a bump-like structure which is not seen in the cross section on the proton. This structure may signal the existence of a relatively narrow ($M\sim 1.68$ GeV, $\Gamma \leq 30$ MeV) baryon state.

6 data tables
Table 1

Quasi free differential cross section for the reaction GAMMA N --> ETA N at COS(THETA(CM)) from -0.9 to -0.5.

Table 2

Quasi free differential cross section for the reaction GAMMA N --> ETA N at COS(THETA(CM)) from -0.3 to 0.1.

Table 3

Quasi free differential cross section for the reaction GAMMA N --> ETA N at COS(THETA(CM)) from 0.1 to 0.5.

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