Exclusive measurement of quasi-free $\mth{\eta}$-photoproduction from deuterium

J. Weiß; P. Achenbach; R. Beck; V. Hejny; V. Kleber; M. Kotulla; B. Krusche; V. Kuhr; R. Leukel; V. Metag; V.M. Olmos de Léon; R.O. Owens; F. Rambo; A. Schmidt; U. Siodlaczek; H. Ströher; F. Wissmann; M. Wolf

doi:doi:10.1140/epja/i2002-10085-9

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Hadrons and Nuclei

Eur. Phys. J. A 16, 275-284 (2003)
DOI: 10.1140/epja/i2002-10085-9

Exclusive measurement of quasi-free $\mth{\eta}$ -photoproduction from deuterium

J. Weiß¹, P. Achenbach², R. Beck², V. Hejny³, V. Kleber³, M. Kotulla¹, B. Krusche⁴, V. Kuhr⁵, R. Leukel², V. Metag¹, V.M. Olmos de Léon¹, R.O. Owens⁶, F. Rambo⁵, A. Schmidt², U. Siodlaczek⁷, H. Ströher³, F. Wissmann⁵ and M. Wolf¹

¹ II. Physikalisches Institut, Justus-Liebig-Universität Gießen, Heinrich-Buff-Ring 16, D-35392 Gießen, Germany
² Institut für Kernphysik, Johannes-Gutenberg-Universität Mainz, Johannes-Joachim-Becher-Weg 45, D-55099 Mainz, Germany
³ Institut für Kernphysik, Forschungszentrum Jülich GmbH, D-52425 Jülich, Germany
⁴ Department für Physik und Astronomie, Universität Basel, Klingelbergstrasse 82, CH-4056 Basel, Switzerland
⁵ II. Physikalisches Institut, Georg-August-Universität Göttingen, Bunsenstr. 7-9, D-37073 Göttingen, Germany
⁶ Department of Physics and Astronomy, University of Glasgow, Glasgow G128QQ, UK
⁷ Physikalisches Institut, Eberhard-Karls-Universität Tübingen, Auf der Morgenstelle 14, D-72076 Tübingen, Germany

Bernd.Krusche@unibas.ch

(Received: 2 September 2002 / Published online: 28 January 2003)

Abstract
Quasi-free photoproduction of $\eta$ -mesons from the deuteron has been measured at the tagged photon facility of the Mainz microtron MAMI with the photon spectrometer TAPS for incident photon energies from the production threshold at 630 MeV up to 820 MeV. In a fully exclusive measurement $\eta$ -mesons and recoil nucleons were detected in coincidence. At incident photon energies above the production threshold on the free nucleon, where final-state interaction effects are negligible, an almost constant ratio of $\sigma_n/\sigma_p=0.66\pm0.10$ was found. At lower incident photon energies the ratio rises due to re-scattering effects. The average ratio agrees with the value extracted from a comparison of the inclusive $d(\gamma ,\eta)X$ cross section to the free-proton cross-section via a participant-spectator model for the deuteron cross-section ( $\sigma_n/\sigma_p=0.67\pm0.07$ ). The angular dependence of the ratio agrees with the expected small deviation of neutron and proton cross-section from isotropy due to the influence of the D₁₃(1520)-resonance. The energy dependence of the ratio in the excitation energy range of the S₁₁(1535)-resonance disfavors model predictions which try to explain this resonance as $K\Sigma$ bound state.