Köln 2004 – scientific programme

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HK: Physik der Hadronen und Kerne

HK 30: Electromagnetic and Hadronic Probes V

HK 30.6: Talk

Wednesday, March 10, 2004, 15:30–15:45, B

Selection rules in η photoproduction — •Olivia Bartholomy — Helmholtz–Institut für Strahlen– und Kernphysik, Nußallee 14–16, 53111 Bonn, Germany

The study of photoproduction reactions off nucleons can help to clarify not yet resolved questions in baryon spectroscopy. Data of the first experimental phase of the CB–ELSA experiment was analyzed with respect to the reaction γ p→ pη. Results [1] on differential cross sections covering photon energies between 0.75 and 3.0 GeV, and thus the whole resonance region, for almost the full solid angle will be presented.

The experimental data served as input for a coupled–channel analysis along with the results obtained for the channel γ p→ pπ⁰ and data from TAPS and GRAAL. The conclusions that can be drawn from the partial–wave analysis reproduce previous experimental findings and known resonance contributions. Along with the states known to couple to Nγ and Nη, evidence was found for a new resonance of J^P=5/2⁻ at (W, Γ)=((2079± 40) MeV, (368₋₅₀⁺¹⁰⁰) MeV). The results on masses, widths, and couplings obtained from the analysis will be discussed.

We observe that the contributing states follow a noticeable pattern: For each given orbital angular momentum from the quark model L=1, 2, and 3, the states with Spin S=1/2 and lowest total angular momentum J=L−S are predominantly excited in the intermediate state of γ p→ pη.

Supported by DFG.

[1] V. Credé, O. Bartholomy et al., hep-ex/0311045, submitted to Phys. Rev. Lett.