Evidence for a narrow structure at W∼1.68 GeV in η photoproduction off the neutron

K0Λ Photoproduction Studied with an Electromagnetic Calorimeter FOREST

“…Many experimental groups have observed a narrow resonance-like structure at the total energy W = 1.67 GeV [7][8][9][10][11][12]. The measured properties are, namely, the centroid of 1.67 GeV and the width of 30 MeV, are in good agreement.…”

Exciting Baryons with MAMI

“…The second exciting observation was a narrow structure in the excitation function of η photoproduction off neutrons at W = 1670 MeV [24][25][26][27]. The position coincides with a dip observed in the γp → ηp total cross section [28] reaction within the Bonn-Gachina model showed that the bump in the total cross section and the behavior of the angular distributions can be understood quantitatively as interference between the two well-known J P = 1/2 − resonances, the N * (1535)1/2 − and the N * (1650)1/2 states, if the sign of the electromagnetic A 1/2 helicity coupling of the N * (1650) is inversed for the neutron with respect to the current PDG entry and to quark model predictions.…”

Production of η and η′ mesons on nucleons and nuclei

“…The first fully exclusive measurement, which already used a complete reconstruction of the final state kinematics to remove the Fermi motion effects, was done in the threshold region [53]. This reaction generated a lot of interest when the first exclusive measurements [54] at higher incident photon energies carried out at the GRAAL facility revealed a pronounced, narrow structure at incident photon energies around 1 GeV, which is absent for the γp → pη reaction. Subsequently, the quasi-free production of η mesons off neutrons was studied in detail with deuteron targets at LNS in Tohoku [55], at ELSA in Bonn [56,43], and at MAMI in Mainz [44,50].…”