Near threshold photoproduction of η-mesons from complex nuclei

Röbig-Landau, M.; Ahrens, J.; Anton, G.; Averbeck, R.; Beck, R.; Fuchs, Markus; Gabler, A.R.; Härter, F.; Harty, P.D.; Hejny, V.; Krusche, B.; MacGregor, I. J. D.; McGeorge, J. C.; Metag, V.; Novotny, R.; Peise, J.; Schubert, András; Simon, R. S.; Ströher, H.

doi:10.1016/0370-2693(96)00125-6

Cited by 90 publications

(92 citation statements)

References 22 publications

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“…In this context it is worth mentioning that according to [2] the mean free path of η mesons in a nuclear medium is about 2 fm, i.e., less than the size of a typical nucleus. A necessary condition for the existence of η-nuclei, hence, appears to be satisfied.…”

Section: Introductionmentioning

confidence: 99%

Low-energy ηd-resonance

et al. 2000

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Elastic ηd scattering is considered within the Alt-Grassberger-Sandhas (AGS) formalism for various ηN input data. A three-body resonant state is found close to the ηd threshold. This resonance is sustained for different choices of the two-body ηN scattering length a ηN . The position of the resonance moves towards the ηd threshold when Re a ηN is increased, and turns into a quasi-bound state at Re a ηN = 0.733 fm.PACS numbers: 25.80.-e, 21.45.+v, 25.10.+s One of the main questions of η-meson physics concerns the existence of η-nuclei, a possibility predicted in a pioneering work by Haider and Liu [1]. In this context it is worth mentioning that according to [2] the mean free path of η mesons in a nuclear medium is about 2 fm, i.e., less than the size of a typical nucleus. A necessary condition for the existence of η-nuclei, hence, appears to be satisfied. A further indication is the observation of pionic nuclei (deeply bound pion states inside nuclei) [3], which were predicted theoretically in [4].Recently, in a number of theoretical investigations based on quite different approaches, such as the mean field approximation [5], the optical model [6], and few-body calculations [7,8], the idea of η-nuclei was given a rather firm ground. Experimentally, after the discouraging attempt of Ref. [9], certain evidence for the existence of η-nuclei was noticed by two groups [10,11]. An additional indication is given by the enhancement of near-threshold η production in the reaction np → dη as reported by the Uppsala group [12]. This observation is most likely to be understood as the effect of a near-threshold bound or resonant ηd state. Moreover, it was suggested [13] that even quite exotic systems containing an η meson and a hyperon (η-hypernuclei) may exist.Being of interest by itself, the existence of η-nuclei would also shed new light on various fundamental problems of particle physics. For example, the study of η-nuclei would give a clue for understanding the possible restoration of chiral symmetry in a nuclear medium, or its partial restoration which may occur at normal densities ∼ 0.17 fm −3 [14][15][16]. A further aspect, which makes such systems interesting for other fields of nuclear physics, is the modification of the two-body ηN force by the nuclear medium. Being enhanced due to the resonant character of the ηN interaction, general properties of such modifications should become particularly evident in this case. Especially, the structure of the S 11 resonance embedded in a nuclear medium may be studied. This would exhibit certain details of the effective Lagrangian models of such a resonance [17], and shed some light, for example, on 1 chiral models which suggest a reduction of its partial width for decaying into the ηN channel [16], or assume S 11 to be a quasi-bound state of the K meson and a Σ hyperon [18]. The interesting suggestion of considering S 11 as a joint manifestation of threshold (casp) and resonance phenomena [19] could also be checked.In a sense, the problem of choosing the most adequa...

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Section: Introductionmentioning

confidence: 99%

Low-energy ηd-resonance

et al. 2000

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“…The situation is completely different for η mesons. Almost independent of their kinetic energy, over a wide range from a few 10 MeV to 1 GeV, the scaling coefficient is close to 2/3 [151,152]. The absorption is large, which means that the meson -nucleon interaction is strong.…”

Section: Inclusive Productionmentioning

confidence: 94%

“…the Glauber-type approximations as in [151] -these can be converted into a meson -nucleon absorption cross section. A convenient technique is the study of the scaling of the meson production cross sections with nuclear mass number A.…”

Section: Inclusive Productionmentioning

confidence: 99%

“…The η-nucleon absorption cross section σ ηN in nuclear matter was determined from such data [151] to be around 30 mb, corresponding to a typical mean free path of λ ≈ 2 fm. For the ω meson an absorption cross section of 70 mb was deduced [154], which is roughly a factor of three larger than the accepted σ ωN cross section for free nucleons.…”

Section: Inclusive Productionmentioning

confidence: 99%

“…We now discuss in greater detail the results for η and η production. Inclusive photoproduction of η mesons from nuclei has been measured for the deuteron [43,51,52,53,55], for 3 He [45], and for heavier nuclei such as 12 C, 40 Ca, 63 Cu, 93 Nb, nat Pb [151,152,158,159] at MAMI, at KEK, in Tohoku, and at ELSA. In general, the agreement between the different measurements is good (see comparisons in [152]).…”

Section: Inclusive Productionmentioning

confidence: 99%

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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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Photoexcitation of baryon resonances on nucleons and nuclei

Krusche

Jaeglé

Mertens

The IVth International Conference on Quarks and Nuclear Physics

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Near threshold photoproduction of η-mesons from complex nuclei

Cited by 90 publications

References 22 publications

Low-energy ηd-resonance

Low-energy ηd-resonance

Production of η and η′ mesons on nucleons and nuclei

Photoexcitation of baryon resonances on nucleons and nuclei

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