Exotic hadron

Short description: Subatomic particles consisting of quarks and gluons

One model of a pentaquark: q is a quark and q an antiquark; gluons (wavy lines) mediate strong interactions between quarks; red, green, and blue color charges must each be present, while the remaining quark and antiquark must share a color and its anticolor, in this example blue and antiblue (shown as yellow).

Exotic hadrons are subatomic particles composed of quarks other than those particles composed of a quark and an anti-quark or of three quarks.[1] By contrast, "ordinary" or "well-known" hadrons such as protons, neutrons contain three quarks and meson pair a quark with an antiquark. Hadrons with explicit valence gluon content would also be considered exotic.[2] In theory, there is no limit on the number of quarks in a hadron, as long as the hadron's color charge is white, or color-neutral.[3]

Consistent with ordinary hadrons, exotic hadrons are classified as being either fermions, like ordinary baryons, or bosons, like ordinary mesons. According to this classification scheme, pentaquarks, containing five valence quarks, are exotic baryons, while tetraquarks (four valence quarks) and hexaquarks (six quarks, consisting of either a dibaryon or three quark-antiquark pairs) would be considered exotic mesons. Tetraquark and pentaquark particles are believed to have been observed and are being investigated; hexaquarks have not yet been confirmed as observed.

Exotic hadrons can be searched for by looking for S-matrix poles with quantum numbers forbidden to ordinary hadrons. Experimental signatures for such exotic hadrons had been seen by 2003 at the latest,[4][5] but they remain a topic of controversy in particle physics.

Jaffe and Low[6] suggested that the exotic hadrons manifest themselves as poles of the P matrix, and not of the S matrix. Experimental P-matrix poles are determined reliably in both the meson–meson channels and nucleon–nucleon channels.

## Contents

* 1 History
* 2 Candidates
* 3 See also
* 4 Notes

## History

When the quark model was first postulated by Murray Gell-Mann and others in the 1960s, it was to organize the states known then to be in existence in a meaningful way. As quantum chromodynamics (QCD) developed over the next decade, it became apparent that there was no reason why only three-quark and quark-antiquark combinations could exist. Indeed, Gell-Mann's original 1964 paper alludes to the possibility of exotic hadrons and classifies hadrons into baryons and mesons depending upon whether they have an odd (baryon) or even (meson) number of valence quarks.[7] In addition, it seemed that gluons, the mediator particles of the strong interaction, could also form bound states by themselves (glueballs) and with quarks (hybrid hadrons). Several decades have passed without conclusive evidence of an exotic hadron that could be associated with the S-matrix pole.

There have been many observations of so-called 'exotic candidates' experimentally observed, which are particles that don't appear to fit the standard quark model. The first few exotic candidates to be identified include the X(3872), which was discovered by the Belle experiment in Japan;[8] the Y(4260) which was discovered at the BaBar experiment;[9] and the Zc+(3900), which was discovered independently by the BES III experiment in China[10] and the Belle experiment.[11]

In April 2014, the LHCb collaboration confirmed the existence of the Z(4430)−, discovered by the Belle experiment, and demonstrated that it must have a minimal quark content of ccdu.[12] Since this was the first exotic hadron to have its quark content experimentally identified, it is also the first unambiguous discovery of an exotic hadron.[13]

In July 2015, LHCb announced the discovery of two particles, named P+c(4380) and P+c(4450), which must have minimal quark content ccuud, making them pentaquarks.[14]

## Candidates

List of exotic hadron candidates  State | Experiments | Notes

|
|

X(3872) | Belle, BaBar, LHCb, CDF, DØ, CMS, ATLAS, BES III | [8]
X(3915) | Belle, BaBar |
X(3940) | Belle |
X(4140) | CDF, CMS, DØ, LHCb |
X(4160) | Belle | [15]
Y(4260) | BaBar, CLEO, Belle | [9]
Y(4220) | BES III, Belle |
X(4274) | CDF, CMS, LHCb |
X(4350) | Belle | [16]
Y(4360) | BaBar, Belle, BES III |
Y(4390) | BES III | [17]
X(4500) | LHCb |
X(4700) | LHCb |
Y(4660) | Belle, BaBar |
X(6900) | LHCb |
Zc+,0(3900) | BES III, Belle | [10][11]
Zc+,0(4020) | BES III |
Z+(4050) | Belle, BaBar |
Z+(4200) | Belle, LHCb |
Z+(4250) | Belle, BaBar |
Z+(4430) | Belle, LHCb |
Pc+(4380) | LHCb |
Pc+(4450) | LHCb |
Yb(10860) | Belle |
Zb+,0(10610) | Belle |
Zb+(10650) | Belle |

## See also

* Exotic matter
* Exotic meson
* Exotic baryon
* Tetraquark
* Pentaquark
* Hexaquark

## Notes

1. ↑ Richard, J.-M. (December 2016). "Exotic Hadrons: Review and Perspectives" (in en). Few-Body Systems 57 (12): 1185–1212. doi:10.1007/s00601-016-1159-0. ISSN 0177-7963. http://link.springer.com/10.1007/s00601-016-1159-0.
2. ↑ Close, F. E. (1988). "Gluonic Hadrons". Reports on Progress in Physics 51 (6): 833–882. doi:10.1088/0034-4885/51/6/002. Bibcode: 1988RPPh...51..833C.
3. ↑ Belz, J., et al. (BNL-E888 Collaboration) (1996). "Search for the weak decay of an H dibaryon". Physical Review Letters 76 (18): 3277–3280. doi:10.1103/PhysRevLett.76.3277. PMID 10060926. Bibcode: 1996PhRvL..76.3277B. "The theory of quantum chromodynamics imposes no specific limitation on the number of quarks composing hadrons other than that they form color singlet states.".
4. ↑ See Tetraquark
5. ↑ "Note on non-q qbar mesons". Journal of Physics G 33: 1. 2006. http://pdg.lbl.gov/2007/reviews/nonqqbar_mxxx050.pdf.
6. ↑ Jaffe, R. L.; Low, F. E. (1979). "Connection between quark-model eigenstates and low-energy scattering". Physical Review D 19 (7): 2105. doi:10.1103/PhysRevD.19.2105. Bibcode: 1979PhRvD..19.2105J.
7. ↑ Gell-Mann, M. (1964). "A Schematic Model of Baryons and Mesons". Physics Letters 8 (3): 214–215. doi:10.1016/S0031-9163(64)92001-3. Bibcode: 1964PhL.....8..214G.
8. ↑ 8.0 8.1 Choi, S.-K.; Olsen, S. L.; Abe, K.; Abe, T.; Adachi, I.; Ahn, Byoung Sup; Aihara, H.; Akai, K. et al. (2003-12-23). "Observation of a Narrow Charmoniumlike State in Exclusive B ± → K ± π + π − J / ψ Decays" (in en). Physical Review Letters 91 (26). doi:10.1103/PhysRevLett.91.262001. ISSN 0031-9007. https://link.aps.org/doi/10.1103/PhysRevLett.91.262001.
9. ↑ 9.0 9.1 Coan, T. E.; Gao, Y. S.; Liu, F.; Artuso, M.; Blusk, S.; Butt, J.; Li, J.; Menaa, N. et al. (2006-04-28). "Charmonium Decays of Y ( 4260 ) , ψ ( 4160 ) , and ψ ( 4040 )" (in en). Physical Review Letters 96 (16). doi:10.1103/PhysRevLett.96.162003. ISSN 0031-9007. https://link.aps.org/doi/10.1103/PhysRevLett.96.162003.
10. ↑ 10.0 10.1 Ablikim, M.; Achasov, M. N.; Ai, X. C.; Albayrak, O.; Ambrose, D. J.; An, F. F.; An, Q.; Bai, J. Z. et al. (2013-06-17). "Observation of a Charged Charmoniumlike Structure in e + e − → π + π − J / ψ at s = 4.26 GeV" (in en). Physical Review Letters 110 (25). doi:10.1103/PhysRevLett.110.252001. ISSN 0031-9007. https://link.aps.org/doi/10.1103/PhysRevLett.110.252001.
11. ↑ 11.0 11.1 Liu, Z. Q.; Shen, C. P.; Yuan, C. Z.; Adachi, I.; Aihara, H.; Asner, D. M.; Aulchenko, V.; Aushev, T. et al. (2013-06-17). "Study of e + e − → π + π − J / ψ and Observation of a Charged Charmoniumlike State at Belle" (in en). Physical Review Letters 110 (25). doi:10.1103/PhysRevLett.110.252002. ISSN 0031-9007. https://link.aps.org/doi/10.1103/PhysRevLett.110.252002.
12. ↑ LHCb collaboration (7 April 2014). "Observation of the resonant character of the Z(4430)− state". Physical Review Letters 112 (22). doi:10.1103/PhysRevLett.112.222002. PMID 24949760. Bibcode: 2014PhRvL.112v2002A.
13. ↑ Closier, Joel (Apr 9, 2014). "Unambiguous observation of an exotic particle which cannot be classified within the traditional quark model" (in en-US). https://lhcb-outreach.web.cern.ch/2014/04/09/unambiguous-observation-of-an-exotic-particle-which-cannot-be-classified-within-the-traditional-quark-model/.
14. ↑ Aaij, R., et al. (LHCb collaboration) (2015). "Observation of J/ψp resonances consistent with pentaquark states in Λ0b→J/ψK−p decays". Physical Review Letters 115 (7). doi:10.1103/PhysRevLett.115.072001. PMID 26317714. Bibcode: 2015PhRvL.115g2001A.0b→J/ψK−p+decays&rft.jtitle=[[Physics:Physical+Review+Letters|Physical+Review+Letters]]&rft.aulast=Aaij&rft.aufirst=R.,+et+al.+(LHCb+collaboration)&rft.au=Aaij, R.,+et+al.+(LHCb+collaboration)&rft.date=2015&rft.volume=115&rft.issue=7&rft_id=info:doi/10.1103/PhysRevLett.115.072001&rft_id=info:pmid/26317714&rft_id=info:bibcode/2015PhRvL.115g2001A&rfr_id=info:sid/en.wikibooks.org:Physics:Exotic_hadron">
15. ↑ Belle Collaboration; Abe, K. (2008-05-19). "Search for new charmonium states in the processes e+ e- → J/psi D(*) D(*) at sqrt{s} ~ 10.6 GeV". Physical Review Letters 100 (20). doi:10.1103/PhysRevLett.100.202001. ISSN 0031-9007. PMID 18518525.
16. ↑ The Belle Collaboration; Shen, C. P. (2010-03-16). "Evidence for a new resonance and search for the Y(4140) in $\gamma \gamma \to \phi J/\psi$". Physical Review Letters 104 (11). doi:10.1103/PhysRevLett.104.112004. ISSN 0031-9007. PMID 20366468.
17. ↑ Ablikim, M.; Achasov, M. N.; Ahmed, S.; Ai, X. C.; Albayrak, O.; Albrecht, M.; Ambrose, D. J.; Amoroso, A. et al. (2017-03-01). "Evidence of Two Resonant Structures in $e^+ e^- \to \pi^+ \pi^- h_c$". Physical Review Letters 118 (9). doi:10.1103/PhysRevLett.118.092002. ISSN 0031-9007. PMID 28306302.

* v
* t
* e

Particles in physics

Elementary|

| Fermions|

| Quarks|

* Up (quark
* antiquark)
* Down (quark
* antiquark)
* Charm (quark
* antiquark)
* Strange (quark
* antiquark)
* Top (quark
* antiquark)
* Bottom (quark
* antiquark)

|

Leptons|

* Electron
* Positron
* Muon
* Antimuon
* Tau
* Antitau
* Electron neutrino
* Electron antineutrino
* Muon neutrino
* Muon antineutrino
* Tau neutrino
* Tau antineutrino

Bosons|

| Gauge|

* Photon
* Gluon
* W and Z bosons

|

Scalar|

* Higgs boson

Ghost fields|

* Faddeev–Popov ghosts

Hypothetical|

| Superpartners|

| Gauginos|

* Gluino
* Gravitino
* Photino

|

Others|

* Higgsino
* Neutralino
* Chargino
* Axino
* Sfermion (Stop squark)

Others|

* Planck particle
* Axion
* Dilaton
* Dual graviton
* Graviton
* Leptoquark
* Majoron
* Majorana fermion
* Magnetic monopole
* Preon
* Sterile neutrino
* Tachyon
* W′ and Z′ bosons
* X and Y bosons

Composite|

| Hadrons|

| Baryons / hyperons|

* Nucleon
* Proton
* Antiproton
* Neutron
* Antineutron
* Delta baryon
* Lambda baryon
* Sigma baryon
* Xi baryon
* Omega baryon

|

Mesons / quarkonia|

* Pion
* Rho meson
* Eta and eta prime mesons
* Phi meson
* J/psi meson
* Omega meson
* Upsilon meson
* Kaon
* B meson
* D meson

Exotic hadrons|

* Tetraquark
* Pentaquark

Others|

* Atomic nuclei
* Atoms
* Exotic atoms
* Positronium
* Muonium
* Tauonium
* Onia
* Superatoms
* Molecules

Hypothetical|

| Hypothetical baryons|

* Hexaquark
* Skyrmion

|

Hypothetical mesons|

* Glueball
* Theta meson
* T meson

Others|

* Mesonic molecule
* Pomeron
* Diquarks

Quasiparticles|

* Davydov soliton
* Dropleton
* Exciton
* Hole
* Magnon
* Phonon
* Plasmaron
* Plasmon
* Polariton
* Polaron
* Roton
* Trion

Lists|

* Baryons
* Mesons
* Particles
* Quasiparticles
* Timeline of particle discoveries

Related|

* History of subatomic physics
* timeline
* Standard Model
* mathematical formulation
* Subatomic particles
* Particles
* Antiparticles
* Nuclear physics
* Eightfold Way
* Quark model
* Exotic matter
* Massless particle
* Relativistic particle
* Virtual particle
* Wave–particle duality
* Particle chauvinism

Wikipedia books|

* Hadronic Matter
* Particles of the Standard Model
* Leptons
* Quarks

Physics portal

0.00

(0 votes)

Original source: https://en.wikipedia.org/wiki/Exotic hadron. Read more

|

Retrieved from "https://handwiki.org/wiki/index.php?title=Physics:Exotic_hadron&oldid=4549394"
*[v]: View this template
*[t]: Discuss this template
*[e]: Edit this template