J.-F. Zhang

Constraining N*(1535) parameters from the eta photoproduction

Abstract Current broad uncertainties on the position, total width and eta branching ratio for N ∗ (1535), reported in the 1996 Particle Data Tables, can be narrowed down considerably utilizing the precise Mainz and Bonn data on eta photoproduction. We obtain here a precise determination of the total width from such a study, fixing other parameters. We find the set of N ∗ (1535) parameters, suggested by the Particle Data Group (PDG), to be inconsistent with the experimental results from η-photoproduction. In particular, values for the photon helicity coupling and/or the eta branching ratio of the resonance, required in order to fit the data, are larger than the PDG values. This result has important consequences for the interpretation of the resonance in the framework of different models, including some exotic possibilities.

Photoproduction of the eta-prime mesons as a new tool to probe baryon resonances

We examine {eta}{prime} photoproduction as a novel tool to study baryon resonances around 2 GeV, of particular interest to the quark shell model, which predicts a number of them. We find important roles of the form factors at the strong vertices, and show that the {ital N}{sup *}(2080) can be probed efficiently by this reaction.

Extraction of the ratio of the N∗ (1535) electromagnetic helicity amplitudes from eta photoproduction off neutrons and protons

Abstract Using the recent precise measurements of eta photoproduction in proton and deuteron targets, we extract the ratio of the helicity amplitudes A 1 2 n A 1 2 p , for the excitation of N ∗ (1535), in the effective Lagrangian approach. It is fairly model-independent, free from the final-state interaction effects, and negative as predicted by the quark models. We stress the importance of polarization observables in further elucidation of the N ∗ (1520) photoexcitation amplitudes.

Model-Independent Extraction of the N*(1535) Electrostrong Form Factor from Eta Electroproduction.

We analyze the existing data on electroproduction of eta mesons in the region of {ital W}{approx_equal}1.5 GeV, and extract an electrostrong form factor for the {ital N}{sup *}(1535) electroexcitation and decay into the {eta}{minus}{ital N} channel, which is found to be relatively insensitive to the uncertainties of the effective Lagrangian approach. This extracted quantity is of interest in the QCD description of relevant baryons. {copyright} {ital 1996 The American Physical Society.}

Photoproduction of {eta} mesons near threshold

A comment on the Letter by B. Krusche, et.al., Phys. Rev. Lett. 74, 3736 (1995). Copyright 1995 The American Physical Society.

Exploring the reaction mechanism of eta prime photoproduction

Abstract We examine theoretical implications of studying the differential cross-section and some key polarization observables in the η′ photoproduction reaction off protons, from its threshold to about 2 GeV of cm energy, the region of the so-called “missing baryon resonances”. We compare implications of different models all of which generate the observed peak in the total η′ photproduction cross section, but have very different differential cross section and polarization profields. Their measurements are thus crucial in distinguishing these reaction mechanisms, of interest to understanding QCD in its nonperturbative domain.