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Eta physics at threshold
Authors:P Moskal  H-H Adam  A Budzanowski  R Czyzykiewicz  D Grzonka  M Janusz  L Jarczyk  B Kamys  A Khoukaz  K Kilian  P Kowina  T Lister  W Oelert  T Rozek  R Santo  G Schepers  T Sefzick  M Siemaszko  J Smyrski  S Steltenkamp  A Strzalkowski  P Winter  M Wolke  P Wüstner  W Zipper
Institution:(1) IKP, Forschungszentrum Jülich, D-52425 Jülich, Germany;(2) M. Smoluchowski Institute of Physics, Jagellonian University, PL-30-059 Kraków, Poland;(3) IKP, Westfälische Wilhelms-Universität, D-48149 Münster, Germany;(4) Institute of Nuclear Physics, PL-31-342 Kraków, Poland;(5) ZEL, Forschungszentrum Jülich, D-52425 Jülich, Germany;(6) Institute of Physics, University of Silesia, PL-40-007 Katowice, Poland
Abstract:The production of $\eta$ - and $\eta^{\prime}$ -mesons in elementary nucleon-nucleon collisions has been investigated at the synchrotrons CELSIUS, COSY and SATURNE. The high-quality proton beam with low emittance and small momentum spread permits to study the creation of these mesons very close to the kinematical threshold, where --due to the rapid growth of the phase space volume-- the total cross-section increases by orders of magnitude over a few MeV range of the excess energy. The magnitude and energy dependence of the total cross-section as well as the occupation distribution of the phase space serve as observables for investigating the mechanisms underlying the production processes and the interaction of mesons with nucleons. The precise data on the $\eta$ and $\eta^{\prime}$ creation via the $pp\to pp \eta(\eta^{\prime})$ reactions allowed to settle the general features of the $\eta$ - and $\eta^{\prime}$ -meson production and revealed the sensitivity of the mentioned observables to the nucleon-nucleon-meson final-state interaction. The particular production properties, like for example, the determination of the dominating exchange processes which lead to the excitation of the S 11 nucleon isobar in the case of $\eta$ creation, must be established by confrontation with other observables. The present status of this investigation with an emphasis on the results of the COSY-11 Collaboration is briefly presented. The available data are interpreted in view of the production mechanism and the meson-nucleon interaction.Received: 30 September 2002, Published online: 22 October 2003PACS: 13.60.Le Meson production - 13.75.-n Hadron-induced low- and intermediate-energy reactions and scattering (energy $\leq 10$ GeV) - 13.85.Lg Total cross sections - 25.40.-h Nucleon-induced reactions
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