Difference between revisions of "GlueX Physics Review Papers"

Review Papers

Recent Review Papers on Hadron Spectroscopy

The Status of Exotic-quantum-number Mesons, Curtis A. Meyer and Yves Van Haarlem, (2010).

• The search for mesons with non-quark-antiquark (exotic) quantum numbers has gone on for nearly thirty years. There currently is experimental evidence of three isospin one states, the π1(1400), the π1(1600) and the π1(2015). For all of these states, there are questions about the identification of these state, and even if some of them exist. In this article, we will review both the theoretical work and the experimental evidence associated with these exotic quantum number states. We find that the π1(1600) could be the lightest exotic quantum number hybrid meson, but observations of other members of the nonet would be useful.
• Baryon Spectroscopy, Eberhard Klempt and Jean Marc Richard, (2009) arXiv.
• About 120 baryons and baryon resonances are known, from the abundant nucleon with u and d light-quark constituents up to the recently discovered Ωb-=bss, and the Ξb-=bsd which contains one quark of each generation. In spite of this impressively large number of states, the underlying mechanisms leading to the excitation spectrum are not yet understood. Heavy-quark baryons suffer from a lack of known spin-parities. In the light-quark sector, quark-model calculations have met with considerable success in explaining the low-mass excitations spectrum but some important aspects like the mass degeneracy of positive-parity and negative-parity baryon excitations are not yet satisfactorily understood. At high masses, above 1.8 GeV, quark models predict a very high density of resonances per mass interval which is not observed. In this review, issues are identified discriminating between different views of the resonance spectrum; prospects are discussed how open questions in baryon spectroscopy may find answers from photo- and electro-production experiments which are presently carried out in various laboratories.
• The Experimental Status of Glueballs, Volker Crede and Curtis A Meyer, Prog. Part. Nucl. Phys. 63 (2009)74-116 arXiv
• Glueballs and other resonances with large gluonic components are predicted as bound states by Quantum Chromodynamics (QCD). The lightest (scalar) glueball is estimated to have a mass in the range from 1 to 2 GeV/c2; a pseudoscalar and tensor glueball are expected at higher masses. Many different experiments exploiting a large variety of production mechanisms have presented results in recent years on light mesons with JPC = 0++, 0-+, and 2++ quantum numbers. This review looks at the experimental status of glueballs. Good evidence exists for a scalar glueball which is mixed with nearby mesons, but a full understanding is still missing. Evidence for tensor and pseudoscalar glueballs are weak at best. Theoretical expectations of phenomenological models and QCD on the lattice are briefly discussed.
• Glueballs, hybrids, multiquarks Experimental facts versus QCD inspired concepts, Eberhard Klempt and Alexander Zaitsev, Phys. Rep. 454 (2007)1–202, arXiv
• Glueballs , hybrids and multiquark states are predicted as bound states in models guided by quantum chromodynamics, 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 σ and κ mesons. The a0(980) and f0(980), discussed extensively in the literature, are reviewed with emphasis on their Janus- like appearance as $K{\bar K}$ molecules, tetraquark states or $q{\bar q}$ mesons. Most exciting is the possibility that the three mesons f0(1370), f0(1500), and f0(1710) might reflect the appearance of a scalar glueball in the world of quarkonia. However, the existence of f0(1370) is not beyond doubt and there is evidence that both f0(1500) and f0(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 η. Three states are reported below 1.5 GeV/c2 whereas quark models expect only one, perhaps two. One of these states, ι(1440), was the prime glueball candidate for a long time. We show that ι(1440) is the first radial excitation of the η meson.
Hybrids may have exotic quantum numbers which are not accessible by $q{\bar q}$ mesons. There are several claims for JPC = 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 in meson spectroscopy.