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 and gluons, but which – unlike "well-known" hadrons such as protons, neutrons and mesons – consist of more than three valence quarks. By contrast, "ordinary" hadrons contain just two or three quarks. Hadrons with explicit valence gluon content would also be considered exotic.[1] 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.[2]
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,[3][4] but they remain a topic of controversy in particle physics.
Jaffe and Low[5] 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.
^Close, F. E. (1988). "Gluonic Hadrons". Reports on Progress in Physics. 51 (6): 833–882. Bibcode:1988RPPh...51..833C. doi:10.1088/0034-4885/51/6/002. S2CID 250819208.
^Belz, J., et al. (BNL-E888 Collaboration) (1996). "Search for the weak decay of an H dibaryon". Physical Review Letters. 76 (18): 3277–3280. arXiv:hep-ex/9603002. Bibcode:1996PhRvL..76.3277B. doi:10.1103/PhysRevLett.76.3277. PMID 10060926. S2CID 15729745. The theory of quantum chromodynamics imposes no specific limitation on the number of quarks composing hadrons other than that they form color singlet states.{{cite journal}}: CS1 maint: multiple names: authors list (link) CS1 maint: numeric names: authors list (link)
^See Tetraquark
^"Note on non-q qbar mesons" (PDF). Journal of Physics G. 33: 1. 2006.
^Jaffe, R. L.; Low, F. E. (1979). "Connection between quark-model eigenstates and low-energy scattering". Physical Review D. 19 (7): 2105. Bibcode:1979PhRvD..19.2105J. doi:10.1103/PhysRevD.19.2105.
Exotichadrons are subatomic particles composed of quarks and gluons, but which – unlike "well-known" hadrons such as protons, neutrons and mesons – consist...
a meson. "Exotic" hadrons, containing more than three valence quarks, have been discovered in recent years. A tetraquark state (an exotic meson), named...
pionium and protonium is important in order to clarify notions related to exotichadrons such as mesonic molecules and pentaquark states. Kaonium, which is a...
existence has been experimentally confirmed that are conjectured to be exotichadrons and within the Standard Model. States of matter that are not commonly...
The Large Hadron Collider (LHC) is the world's largest and highest-energy particle collider. It was built by the European Organization for Nuclear Research...
theory of strong interactions. A tetraquark state is an example of an exotichadron which lies outside the conventional quark model classification. A number...
charged particles ExotichadronExotic baryon, bound states of 3 quarks and additional particles Exotic meson, non-quark model mesons Exotic matter, a hypothetical...
also conjectures about other exotichadrons in which real gluons (as opposed to virtual ones found in ordinary hadrons) would be primary constituents...
the properties these constituent quarks confer. The existence of "exotic" hadrons with more valence quarks, such as tetraquarks ( q q q q ) and pentaquarks...
neutrons. Most hadrons do not live long enough to bind into nucleus-like composites; those that do (other than the proton and neutron) form exotic nuclei. Any...
quark–antiquark pair and one or more gluons. All exotic mesons are classed as mesons because they are hadrons and carry zero baryon number. Of these, glueballs...
six quarks and six leptons. Quarks are the fundamental constituents of hadrons and interact via the strong force. Quarks are the only known carriers of...
neutral, or "white" for analogy with mixing the primary colors. More exotichadrons can have other types, arrangement or number of quarks (tetraquark, pentaquark)...
as having been likely detected by the two main experiments at the Large Hadron Collider (ATLAS and CMS). The Standard Model is widely considered to be...
In particle physics, exotic baryons are a type of hadron (bound states of quarks and gluons) with half-integer spin, but with a quark content different...
is also able to perform measurements of production cross sections, exotichadron spectroscopy, charm physics and electroweak physics in the forward region...
of 0, and antibaryons (three antiquarks) have a baryon number of −1. Exotichadrons like pentaquarks (four quarks, one antiquark) and tetraquarks (two quarks...
'regular' hadrons are well documented and characterized; however, there is nothing in theory to prevent quarks from forming 'exotic' hadrons such as tetraquarks...
of an electron and its anti-particle, a positron, bound together into an exotic atom, specifically an onium. Unlike hydrogen, the system has no protons...
being performed at the BaBar, Belle and LHCb experiments. Some of the hadrons containing bottom quarks include: B mesons contain a bottom quark (or its...
particle. Strange quarks are found in subatomic particles called hadrons. Examples of hadrons containing strange quarks include kaons ( K ), strange D mesons...
valence quarks, conventionally three. Baryons belong to the hadron family of particles; hadrons are composed of quarks. Baryons are also classified as fermions...
Dineutron, an unstable dibaryon. Diproton, another unstable dibaryon. Exotichadron Pentaquark "Oddball sexaquark particles could be immortal, if they exist...
Understanding bound states of hadrons such as pionium and protonium is also important in order to clarify notions related to exotichadrons such as mesonic molecules...
belongs to the class of matter particles. D. Green (2005). High PT physics at hadron colliders. Cambridge University Press. p. 23. ISBN 978-0-521-83509-1. L...
they can never be observed as free particles due to being confined within hadrons, and hence their presumed lack of rest mass cannot be confirmed by any...
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