GlueX Physics Review Papers

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GlueX Physics

Review Papers

Summer School Lectures

  • Light and Exotic Mesons, Curtis A. Meyer, (1999) DocDb.
    • In this series of lectures I want to provide an overview of the field of light-quark meson spectroscopy. What do we understand about mesons? What does studying mesons tell us about QCD? How do we study mesons? Why do we study mesons; what is exciting about this? The area of light-quark meson spectroscopy deals with mesons built up from u, d, and s quarks. Typically, these systems have masses below 2.5GeV/c2.

Recent Review Papers on Hadron Spectroscopy

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

Older Review Articles

  • Everything About Reggeons, Eugene Levin (1997) arXiv.
    • This is the first part of my lectures on the Pomeron structure which I am going to read during this academic year at the Tel Aviv university. The main goal of these lectures is to remind young theorists as well as young experimentalists of what are the Reggeons that have re-appeared in the high energy phenomenology to describe the HERA and the Tevatron data. Here, I show how and why the Reggeons appeared in the theory, what theoretical problems they have solved and what they have failed to solve. I describe in details what we know about Reggeons and what we do not. The major part of these lectures is devoted to the Pomeron structure, to the answer to the questions: what is the so called Pomeron; why it is so different from other Reggeons and why we have to introduce it. In short, I hope that this lectures will be the shortest way to learn everything about Reggeons from the beginning to the current understanding. I concentrate on the problem of Reggeons in this lectures while the Reggeon interactions or the shadowing corrections I plan to discuss in the second part of my lectures. I include here only a short lecture with an outline of the main properties of the shadowing corrections to discuss a correct (from the point of the Reggeon approach) strategy of the experimental investigation of the Pomeron structure.
  • Proton - anti-proton annihilation and meson spectroscopy with the crystal barrel, Claude Amsler, Rev. Mod. Phys. 70, 1293, (1998) Science DirectarXiv:
    • This report reviews the achievements of the Crystal Barrel experiment at the Low Energy Antiproton Ring (LEAR) at CERN. During seven years of operation Crystal Barrel has collected very large statistical samples in pbarp annihilation, especially at rest and with emphasis on final states with high neutral multiplicity. The measured rates for annihilation into various two-body channels and for electromagnetic processes have been used to test simple models for the annihilation mechanism based on the quark internal structure of hadrons. From three-body annihilations three scalar mesons, a0(1450), f0(1370) and f0(1500) have been established in various decay modes. One of them, f0(1500), may be identified with the expected ground state scalar glueball.

Exotic Quantum Number Mesons

Lattice QCD Calculations


Strong Decay Models