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Hejny, V.; Weiss, Jeffrey M.; Achenbach, P.; Ahrens, J.; Annand, J. R. M.; Beck, Robin A.; Kotulla, M.; Krusche, B.; Kuhr, V.; Leukel, R.; MacGregor, I. J. D.; Metag, V.; Novotny, R.; León, Vladimir; Rambo, F.; Schmidt, Axel; Schumacher, M.; Siodlaczek, U.; Stroeher, H.; Wissmann, F.; Wolf, Michael M.

doi:10.1007/s10050-002-8779-0

Cited by 30 publications

(74 citation statements)

References 11 publications

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“…13 indicates that first order rescattering still fails to explain quantitatively the enhancement of the data right above threshold. This is corroborated by very recent more precise near-threshold data of Hejny et al 12 . For this reason, we then have performed a three-body treatment of the final state interaction 10 , because the very strong effect in first order rescattering suggests that a genuine three-body treatment is required.…”

Section: Final State Interaction In Incoherent Eta Photoproductionsupporting

confidence: 75%

Present Status of Electromagnetic Reactions on the Deuteron Above Pion Threshold

et al. 2003

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The present status of the theoretical description of electromagnetic reactions on the deuteron above pion threshold is reviewed. Three major topics are considered: (i) retardation effects in π-meson exchange contributions to N N -interaction and meson exchange currents in deuteron photodisintegration above π-threshold in the ∆-resonance region, (ii) off-shell effects in the one-body current treated in a simple pion cloud model in deuteron photodisintegration in and above the ∆-resonance region, and (iii) final state interaction effects in photoproduction of π and η mesons on the deuteron. IntroductionIn view of the fact that at present QCD in the non-perturbative regime can at best be described by effective degrees of freedom only, one uses a framework with meson, nucleon and isobar degrees of freedom. Hadron properties are either described phenomenologically or by effective quark models. The central question then is: How accurate is this effective description, and where is the borderline beyond which explicit quark-gluon degrees of freedom have to be considered? It is very likely that no clear cut answer exists.However, the study of electromagnetic reactions on few-nucleon systems may give at least a partial answer because lightest nuclei (deuteron, helium-3) allow reliable theoretical descriptions, and approximations, which are unavoidable in more complex many-body systems, are not necessary. Therefore, such systems constitute reliable test laboratories for the investigation of effective degrees of freedom. Furthermore, the electromagnetic interaction is well known and sufficiently weak, in order to allow conclusive interpretations in terms of charge and current matrix elements. Finally, reactions above pion threshold are of particular interest with respect to explicit meson degrees of freedom and internal baryon structure.The main points of interest are (i) the role of meson and isobar degrees of freedom in medium energy reactions, (ii) many-body phenomena, induced by the effective description in terms of meson, nucleon and isobar d.o.f., e.g., the role of pion retardation in N N interaction and two-body meson exchange operators, and (iii) properties of the neutron like, e.g., the elementary π and η photoproduction on the neutron, in other words, the use of light nuclei as effective neutron targets. Particularly suited are quasifree reactions on the deuteron in order to minimize final

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Section: Final State Interaction In Incoherent Eta Photoproductionsupporting

confidence: 75%

Present Status of Electromagnetic Reactions on the Deuteron Above Pion Threshold

et al. 2003

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“…Sokol and Pavlyuchenko [23] claim an enhancement above background from quasi-free pion production for certain kinematic conditions. Suggestions for the existence of very light η-mesic states, in particular involving helium or tritium nuclei, were later based on results from refined analyses of the η-nucleon, η-nucleus scattering length (see [24] for a summary), using precise data from threshold η-photoproduction off the proton [25], the deuteron [26,27,28,29], and helium nuclei [30,31]. Such states have been in particular sought in the threshold behavior of hadron and photon induced η-production reactions from light nuclei, following the conjecture that a resonant state close to production threshold will enhance the cross section with respect to phase-space expectations.…”

Section: Meson Photoproduction Off Heavier Nucleimentioning

confidence: 99%

Photoproduction of Mesons off Nuclei - The Photonuclear Programs at ELSA and MAMI

Krusche

2012

J. Phys.: Conf. Ser.

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Abstract. Recent results for the photoproduction of mesons from nuclei with tagged bremsstrahlung beams are summarized. The experiments have been done at the Mainz MAMI accelerator with the Crystal Ball/TAPS setup and at the Bonn ELSA accelerator with the Crystal Barrel/TAPS detector. Two main physics topics are covered. The electromagnetic excitation spectrum of the neutron has been studied with meson photoproduction reactions off quasi-free neutrons from light nuclei. Particularly interesting results have been obtained for η-photoproduction, where the excitation function of the neutron shows a pronounced, narrow structure which is not observed for the proton. The interaction of mesons with nuclear matter and the in-medium properties of hadrons under various aspects have been studied with meson photoproduction from nuclei, covering a large mass range (from the deuteron to lead). Questions like the possible formation of η-mesic nuclei and in-medium modifications of the σ-meson have been addressed.

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“…In the case of η photoproduction, the situation is particularly unfavourable. For spin J = 0 nuclei, such as 4 He, coherent photoproduction of pseudoscalar mesons in relative s-wave is forbidden due to spin/parity conservation; even very close to the production threshold only breakup reactions contribute [177,178]. Furthermore, due to the quantum numbers of the dominating amplitude, which is the isovector component of the E 0+ multipole (from the excitation of the S 11 (1535) resonance), there are large cancellations even when J = 0.…”

Section: Coherent Production 321 Single η-Production Off 3 He and 7mentioning

confidence: 99%

Production of η and η′ mesons on nucleons and nuclei

Krusche¹,

Wilkin²

2015

Progress in Particle and Nuclear Physics

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The production of η and η mesons in photon-and hadron-induced reactions on free and quasifree nucleons and on nuclei is reviewed. The extensive database on γN → ηN , for both proton and neutron targets, is described in detail and its implications for the search for N resonances much heavier than the dominant S 11 (1535) discussed. Though less is currently known about the production of the η or of ηπ pairs, these also offer tantalizing prospects in the search for the missing isobars. The more limited data available on pion-induced production are still necessary ingredients in the partial wave analysis discussed.The production of the η-meson in pp and pn collisions shows once again the strong influence of the S 11 (1535) isobar, which is in contrast to the relatively weak behaviour seen near threshold for η production. This difference is reflected in the important final state interaction effects of the η in nuclei that may even lead to this meson being "bound" in some systems. The evidence for this is reviewed for both γA and pA collisions. The inclusive photoproduction of η, η , and ηπ pairs from nuclei provides further information regarding the production mechanism and the interaction of the η and η with nuclei and the ηπ pairs may even allow access to low mass ηA systems that are forbidden in direct single-meson photoproduction.

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Cited by 30 publications

References 11 publications

Present Status of Electromagnetic Reactions on the Deuteron Above Pion Threshold

Present Status of Electromagnetic Reactions on the Deuteron Above Pion Threshold

Photoproduction of Mesons off Nuclei - The Photonuclear Programs at ELSA and MAMI

Production of η and η′ mesons on nucleons and nuclei

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