η-meson photoproduction andN* resonances

Abstract

We investigate the η photoproduction using the effective Lagrangian approach at the tree level. We focus on the new nucleon resonance N * (1675), which was reported by the GRAAL, CB-ELSA and Tohoku LNS, testing its possible spin and parity states theoretically (J P = 1/2 ± , 3/2 ± ). In addition, we include six nucleon resonances, D 13 (1520), S 11 (1535), S 11 (1650), D 15 (1675), P 11 (1710), P 13 (1720) as well as the possible background contributions. We calculate various cross sections including beam asymmetries for the neutron and proton targets. We find noticeable isospin asymmetry in transition amplitudes for photon and neutron targets. This observation may indicate that the new resonance can be identified as a non-strangeness member of the baryon antidecuplet.

Λ(1520)photoproduction off a proton target with Regge contributions

“…[31], we only choose D 13 (2080) with the two-star confirmation ( * * ) but neglect S 11 (2080) and D 15 (2200) because that S 11 is still in poor confirmation ( * ), as for D 15 , we do not have experimental data for the helicity amplitudes which are necessary to determine the strength of the transition γN → N * [26]. Moreover the spin 5/2 Lorentz structure of D 15 bring theoretical uncertainties [33]. In the quark model of Ref.…”

Axial charges of octet and decuplet baryons

“…For the J = 1 2 , 3 2 , and 5 2 baryons with four-momentum P and energy E = M 2 + P 2 we employ Dirac and spinors, similar as in ref. [38], as follows:…”

On the couplings in ELA for eta-meson photoproduction

“…As for the form factor for u-channel, there has been no well established rule, thus we follow Ref. [2] to use the same cut-off (0.9 GeV) for both the sand u-channel. Due to the small absolute value of u (also a small angular dependence), this form factor f (u) almost kills Z(u)-R. In this way all the contributing factors to the equivalence-breaking terms are greatly reduced, thus an effective PS-PV equivalence is obtained.…”

“…On the theory side the Effective Lagrangian Approach (ELA) has shown its effectiveness and relative simplicity in interpreting data. However, in the application of ELA there exists an ambiguity concerning the couplings: while some authors use the pseudo-scalar (PS) coupling only [2], the others employ both the PS and the PV couplings [3], thus an in-depth study is needed for revealing the characteristics of the two couplings.…”