S-wave γγ→ππ and f[sub 0](980)→ππ

Oller, J. A.; Roca, L.; Schat, Carlos; Rupp, George; Beveren, Eef van; Bicudo, Pedro; Hiller, Brigitte; Kleefeld, Frieder

doi:10.1063/1.2973490

Cited by 24 publications

(68 citation statements)

References 16 publications

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“…Applied to the (485), the direct answer from its 2-photon coupling assigns a qq nature [1115]. Using dispersion relations, Oller et al determine ( → ) = 1.5 ± 0.3 KeV/c 2 and argue that this widths may be too low for aqq resonance and suggest the (485) to be a tetraquark resonance or to have an important glueball component [1116]. Mennessier et al confirm that the (485) can have a large gluonium component in its wave function [1117].…”

Section: Scalar Mesons In 2-photon Fusionmentioning

confidence: 97%

Glueballs, hybrids, multiquarks

2007

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Glueballs, hybrids and multiquark states are predicted as bound states in models guided by quantum chromo dynamics (QCD), by QCD sum rules or QCD on a lattice. Estimates for the (scalar) glueball ground state are in the mass range from 1000 to 1800 MeV, followed by a tensor and a pseudoscalar glueball at higher mass. Experiments have reported evidence for an abundance of meson resonances with 0 −+ , 0 ++ and 2 ++ quantum numbers. In particular, the sector of scalar mesons is full of surprises starting from the elusive and mesons. The a 0 (980) and f 0 (980), discussed extensively in the literature, are reviewed with emphasis on their Janus-like appearance as KK molecules, tetraquark states or qq mesons. Most exciting is the possibility that the three mesons f 0 (1370), f 0 (1500), and f 0 (1710) might reflect the appearance of a scalar glueball in the world of quarkonia. However, the existence of f 0 (1370) is not beyond doubt and there is evidence that both f 0 (1500) and f 0 (1710) are flavour octet states, possibly in a tetraquark composition. We suggest a scheme in which the scalar glueball is dissolved into the wide background into which all scalar flavour-singlet mesons collapse.There is an abundance of meson resonances with the quantum numbers of the . Three states are reported below 1.5 GeV/c 2 whereas quark models expect only one, perhaps two. One of these states, (1440), was the prime glueball candidate for a long time. We show that (1440) is the first radial excitation of the meson.Hybrids may have exotic quantum numbers which are not accessible by qq mesons. There are several claims for J P C = 1 −+ exotics, some of them with properties as predicted from the flux tube model interpreting the quark-antiquark binding by a gluon string. The evidence for these states depends partly on the assumption that meson-meson interactions are dominated by s-channel resonances. Hybrids with non-exotic quantum numbers should appear as additional states. Light-quark mesons exhibit a spectrum of (squared) masses which are proportional to the sum of orbital angular momentum and radial quantum numbers. Two states do not fall under this classification. They are discussed as hybrid candidates.The concept of multiquark states has received revived interest due to new resonances in the spectrum of states with open and hidden charm. The new states are surprisingly narrow and their masses and their decay modes often do not agree with simple quark-model expectations.Lattice gauge theories have made strong claims that glueballs and hybrids should appear in the meson spectrum. However, the existence of a scalar glueball, at least with a reasonable width, is highly questionable. It is possible that hybrids will turn up in complex multibody final states even though so far, no convincing case has been made for them by experimental data. Lattice gauge theories fail to identify the nonet of scalar mesons. Thus, at the present status of approximations, lattice gauge theories seem not to provide a trustworthy guide into unknown territory ...

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Section: Scalar Mesons In 2-photon Fusionmentioning

confidence: 97%

Glueballs, hybrids, multiquarks

2007

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“…If one aims at a description of the whole reaction A + B → γ + B one has to be aware of the possible non-resonant term. But this is a different issue [45]. In the following we will always start with the general formula K γ GΓ † R .…”

Section: Appendix Bmentioning

confidence: 98%

On the radiative decays of light vector and axial-vector mesons

2008

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We study the light vector and axial-vector mesons. According to the hadrogenesis conjecture the nature of the two types of states is distinct. The axial-vector mesons are generated dynamically by coupled-channel interactions based on the chiral Lagrangian written down in terms of the Goldstone bosons and the light vector mesons. We propose a novel counting scheme that arises if the chiral Lagrangian is supplemented by constraints from large-N_c QCD in the context of the hadrogenesis conjecture. The counting scheme is successfully tested by a systematic study of the properties of vector mesons. The spectrum of light axial-vector mesons is derived relying on the leading order interaction of the Goldstone bosons with the vector mesons supplemented by a phenomenology for correction terms. The f_1(1282), b_1(1230), h_1(1386), a_1(1230) and K_1(1272) mesons are recovered as molecular states. Based on those results the one-loop contributions to the electromagnetic decay amplitudes of axial-vector molecules into pseudo-scalar or vector mesons are evaluated systematically. In order to arrive at gauge invariant results in a transparent manner we choose to represent the vector particles by anti-symmetric tensor fields. It is emphasized that there are no tree-level contributions to a radiative decay amplitude of a given state if that state is generated by coupled-channel dynamics. The inclusion of the latter would be double counting. At present we restrict ourselves to loops where a vector and a pseudo-scalar meson couple to the axial-vector molecule. We argue that final and predictive results require further computations involving intermediate states with two vector mesons. The relevance of the latter is predicted by our counting rules.Comment: added appendix concerning double-counting issue

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“…where s IV a0 was obtained in Section II C. The analytical continuation in the complex s-plane can be performed using the unitarity relation (similar to how it was done for the case of the second (II) Riemann sheet in [58]),…”

Section: A γγ → πη Kk Cross Sectionsmentioning

confidence: 99%

Theoretical analysis of the γγ→π0η process

Danilkin¹,

Deineka²,

Vanderhaeghen³

2017

Phys. Rev. D

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We present a theoretical study of the γγ → πη process from the threshold up to 1.4 GeV in the πη invariant mass. For the s-wave a0(980) resonance state we adopt a dispersive formalism using a coupled-channel Omnès representation, while the d-wave a2(1320) state is described as a Breit-Wigner resonance. An analytic continuation to the a0(980) pole position allows us to extract its two-photon decay width as Γa 0 →γγ = 0.27(4) keV.

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S-wave γγ→ππ and f[sub 0](980)→ππ

Cited by 24 publications

References 16 publications

Glueballs, hybrids, multiquarks

Glueballs, hybrids, multiquarks

On the radiative decays of light vector and axial-vector mesons

Theoretical analysis of the γγ→π0η process

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