Impressions of the Meson Spectrum: Hybrids &amp; Exotics, present and future

Pennington, M.R.

doi:10.1051/epjconf/201611301014

Cited by 4 publications

(4 citation statements)

References 62 publications

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“…Very much along the same lines, but much earlier, a hybrid interpretation was advanced for the J PC = 1 −− state Y (4260), which has a small e + e − annihilation cross section [51,312,313]. In the meanwhile, hybrids have been offered as templates for other exotic hadrons as well [314,315]. They have been put on firmer theoretical footings in the framework of effective field theories [316].…”

Section: Tetraquarks As Hybridsmentioning

confidence: 96%

Exotics: Heavy pentaquarks and tetraquarks

Ali¹,

Lange

Stone

2017

Progress in Particle and Nuclear Physics

563

402

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For many decades after the invention of the quark model in 1964 there was no evidence that hadrons are formed from anything other than the simplest pairings of quarks and antiquarks, mesons being formed of a quark-antiquark pair and baryons from three quarks. In the last decade, however, in an explosion of data from both e + e − and hadron colliders, there are many recently observed states that do not fit into this picture. These new particles are called generically "exotics". They can be either mesons or baryons. Remarkably, they all decay into at least one meson formed of either a cc or bb pair. In this review, after the introduction, we explore each of these new discoveries in detail first from an experimental point of view, then subsequently give a theoretical discussion. These exotics can be explained if the new mesons contain two-quarks and twoantiquarks (tetraquarks), while the baryons contain four-quarks plus an antiquark (pentaquarks). The theoretical explanations for these states take three divergent tracks: tightly bound objects, just as in the case of normal hadrons, but with more constituents, or loosely bound "molecules" similar to the deuteron, but formed from two mesons, or a meson or baryon, or more wistfully, they are not multiquark states but appear due to kinematic effects caused by different rescatterings of virtual particles; most of these models have all been post-dictions. Both the tightly and loosely bound models predict the masses and related quantum numbers of new, as yet undiscovered states. Thus, future experimental discoveries are needed along with theoretical advances to elucidate the structure of these new exotic states.

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Section: Tetraquarks As Hybridsmentioning

confidence: 96%

Exotics: Heavy pentaquarks and tetraquarks

Ali¹,

Lange

Stone

2017

Progress in Particle and Nuclear Physics

563

402

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show abstract

“…Hybrids are hadrons formed from the valence quarks and gluons, for example, consisting of qqg. In the context of the X, Y, Z hadrons, hybrids have been advanced as a model for the J PC = 1 −− state Y (4260), which has a small e + e − annihilation cross section [11][12][13] , But, hybrids have been offered as templates for other exotic hadrons as well 14,15 .…”

Section: Arxiv:160505954v1 [Hep-ph] 19 May 2016mentioning

confidence: 99%

Multiquark Hadrons — A New Facet of QCD

Ali

2018

Mathematical Physics

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I review some selected aspects of the phenomenology of multiquark states discovered in high energy experiments. They have four valence quarks (called tetraquarks) and two of them are found to have five valence quarks (called pentaquarks), extending the conventional hadron spectrum which consists of quark-antiquark (qq) mesons and qqq baryons. Multiquark states represent a new facet of QCD and their dynamics is both challenging and currently poorly understood. I discuss various approaches put forward to accommodate them, with emphasis on the diquark model.

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“…In particular, a number of unexpected states have been observed, e.g. various charmonium and bottomonium-like structures ("X, Y, Z 's") and the charm-strange D s0 (2317) [49,53], and there are also longer-standing puzzles such as the makeup of the light scalar mesons [55,57]. There has been a lot of theoretical work and speculation about their nature [6,50]-possibilities include tetraquarks (containing two quarks and two antiquarks), molecular states of hadrons, hadro-quarkonia and hybrid mesons (where the gluonic field is excited).…”

Section: Introductionmentioning

confidence: 99%

Untitled

Thomas¹

2018

Light Cone 2016

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Some recent progress in using lattice QCD to perform first-principles calculations of the spectra of mesons is discussed. In particular, I highlight some new results on resonances, near-threshold states and related scattering phenomena-this is a theoretically and experimentally interesting area where we have made significant advances in the last few years.This article belongs to the Topical Collection "Light Cone 2016".

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Impressions of the Meson Spectrum: Hybrids & Exotics, present and future

Cited by 4 publications

References 62 publications

Exotics: Heavy pentaquarks and tetraquarks

Exotics: Heavy pentaquarks and tetraquarks

Multiquark Hadrons — A New Facet of QCD

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