The case of the pseudoscalar glueball

Masoni, A.; Cicalò, C.; Usai, G. L.

doi:10.1088/0954-3899/32/9/r01

Cited by 63 publications

(78 citation statements)

References 105 publications

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“…The radial excitation (1295) is not seen in this reaction; hence the (1440) must have a different nature. At that time it was proposed (and often still is [1,[1001][1002][1003][1004]) to be a glueball.…”

Section: The (1440)mentioning

confidence: 99%

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: The (1440)mentioning

confidence: 99%

Glueballs, hybrids, multiquarks

2007

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“…A review on the experimental status of the qq is given in Ref. [19]. However, this state lies considerably lower than the theoretical expectations: the lattice QCD predictions suggest a glueball around 2.5 GeV [36,59]; the mass scale of the pseudoscalar glueball obtained in the QCD sum rule approach is above 2 GeV [7,15,16,60].…”

Section: Conclusion and Discussionmentioning

confidence: 98%

“…Later, in the mass region of the first radial excitation of the η and η ′ mesons, a supernumerous candidate, the η(1405) has been observed. It seems to be clear that η(1405) is allowed as a glueball dominated state mixed with isoscalar qq states due to its behavior in production and decays, namely, it has comparably large branching ratios in the J/ψ radiativedecay, but it has not been observed in γγ collisions [19,55,58]. A review on the experimental status of the qq is given in Ref.…”

Section: Conclusion and Discussionmentioning

confidence: 99%

“…The research of glueballs may give a unique insight into the non-Abelian dynamics of QCD. Theoretical investigations including lattice simulations [1][2][3], model researches [4][5][6] and sum rule analyses [7][8][9][10][11][12][13][14][15][16][17][18] have been going on for a long time, but no decisive evidence of the existence of glueballs has been confirmed by experimental research up to now [19,20]. Further investigation on glueballs still makes sense.…”

Section: Introductionmentioning

confidence: 99%

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Finite-width Laplacian sum rules for 2++ tensor glueball in the instanton vacuum model

Chen

Liu

2017

Phys. Rev. D

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The more-carefully defined, and more appropriate 2 ++ tensor glueball current is a SUc(3) gaugeinvariant, symmetric, traceless and conserved Lorentz-irreducible tensor. After Lorentz decomposition, the invariant amplitude of the correlation function is abstracted, and calculated based on the semiclassical expansion for quantum chromodynamics (QCD) in the instanton liquid background. Besides taking the perturbative contribution into account, we calculate the contribution arising from the interaction (or the interference) between instantons and the quantum gluon fields, which is infrared free. Instead of the usual zero-width approximation for the resonances, the Breit-Wigner form with a correct threshold behavior for the spectral function of the finite-width three resonances is adopted. The properties of the 2 ++ tensor glueball are investigated via a family of the QCD Laplacian sum rules for the invariant amplitude. The values of the mass, decay width and coupling constants for the 2 ++ resonance in which the glueball fraction is dominant are obtained.

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“…These states were widely studied in the past to disentangle between their production and that of η excitations, which could possibly carry exotic quantum numbers. Many observation of η's and f 1 mesons have been reported since the Sixties, when the issue of the overlap of many axial and pseudoscalar states and the difficulty of their identification posed the so-called E/ι puzzle [17]. While annihilation experiments, and in particular OBELIX, could provide a solution to this puzzle addressing the production of several pseudoscalar and axial states, high statistics photoproduction reactions are expected to provide new complementary information which will be able to improve the knowledge in this sector.…”

Section: Epj Web Of Conferencesmentioning

confidence: 99%

The Meson Spectroscopy Program at the Jefferson Laboratory

Filippi

2015

EPJ Web of Conferences

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Abstract. The experimental techniques that will be applied by the next generation meson spectroscopy experiments at JLab are described. For the first time, these experiments will be able to exploit the features of a photon beam of unprecedented intensity and momentum resolution, that will allow to perform precision studies of meson states with masses below 3 GeV/c 2 . Photon induced reactions will enhance the production of spin-1 mesons, that are of particular interest according to the most recent Lattice QCD calculations of the lightest exotic hybrid meson.

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The case of the pseudoscalar glueball

Cited by 63 publications

References 105 publications

Glueballs, hybrids, multiquarks

Glueballs, hybrids, multiquarks

Finite-width Laplacian sum rules for 2++ tensor glueball in the instanton vacuum model

The Meson Spectroscopy Program at the Jefferson Laboratory

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