GAMMA N --> ETA N
Electron production
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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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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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