η-nucleon scattering length and effective range

Green, Anthony M.; Wycech, S.

doi:10.1103/physrevc.55.r2167

Cited by 88 publications

(147 citation statements)

References 20 publications

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“…Further information is found in Ref. [18]. An energy dependence of a so deduced elastic T matrix is shown further down with other results in Fig.…”

Section: ηN Scatteringsupporting

confidence: 77%

Search for quasi boundηmesons

Machner

2015

J. Phys. G: Nucl. Part. Phys.

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The search for a quasi bound η meson in atomic nuclei is reviewed. This tentative state is studied theoretically as well as experimentally. The theory starts from elastic η nucleon scattering which is derived from production data within some models. From this interaction the η nucleus interaction is derived. Model calculations predict binding energies and widths of the quasi bound state. Another method is to derive the η nucleus interaction from excitation functions of η production experiments. The s wave interaction is extracted from such data via final state interaction theorem. We give the derivation of s wave amplitudes in partial wave expansion and in helicity amplitudes and their relation to observables. Different experiments extracting the final state interaction are discussed as are production experiments. So far only three experiments give evidence for the existence of the quasi bound state: a pion double charge exchange experiment, an effective mass measurement, and a transfer reaction at recoil free kinematics with observation of the decay of the state.

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“…Further information is found in Ref. [18]. An energy dependence of a so deduced elastic T matrix is shown further down with other results in Fig.…”

Section: ηN Scatteringsupporting

confidence: 77%

Search for quasi boundηmesons

Machner

2015

J. Phys. G: Nucl. Part. Phys.

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“…However, both experimental values and theoretical predictions for these two quantities have been very contradictory in the literatures [1,15,32,33].…”

Section: A Database and Adjustable Parametersmentioning

confidence: 99%

Quark model approach to the $\eta$ meson electroproduction on the proton

Zhao

Saghai

2002

J. Phys. G: Nucl. Part. Phys.

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A recently developed quark model approach to pseudoscalar meson photoproduction is extended to electroproduction process for the η meson in the kinematics of momentum transfer Q 2 ≤ 4 (GeV/c) 2 and total center of mass energy W ≤ 1.6 GeV. Existing data are well reproduced and the roles of the S 11 (1535) and D 13 (1520) resonances are closely investigated. In the study of the longitudinal excitation of the S 11 (1535) resonance, a reliable constraint on the S 11 (1535) properties is obtained by cleanly removing the electromagnetic transition from the γ (v) p → S 11 (1535) → ηp amplitude. Thus, the fitted quantities can be determined with an uncertainty of about 15%. This could be the first direct constraint on the S 11 (1535) properties in theory.

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“…But for Re a ηN the estimates are still very different (compare, for example, Refs. [26] and [27]). We, therefore, fixed Im a ηN to 0.3 fm and did calculations for several values of Re a ηN within the above interval.…”

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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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η-nucleon scattering length and effective range

Cited by 88 publications

References 20 publications

Search for quasi boundηmesons

Search for quasi boundηmesons

Quark model approach to the $\eta$ meson electroproduction on the proton

Low-energy ηd-resonance

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