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An onium (plural: onia) is a bound state of a particle and its antiparticle.^[1] These states are usually named by adding the suffix -onium to the name of one of the constituent particles (replacing an -on suffix when present), with one exception for "muonium"; a muon–antimuon bound pair is called "true muonium" to avoid confusion with old nomenclature.^[a]

Examples

Positronium is an onium which consists of an electron and a positron bound together as a long-lived metastable state. Positronium has been studied since the 1950s to understand bound states in quantum field theory. A recent development called non-relativistic quantum electrodynamics (NRQED) used this system as a proving ground.^[2]

Pionium, a bound state of two oppositely-charged pions, is interesting for exploring the strong interaction. This should also be true of protonium. The true analogs of positronium in the theory of strong interactions are the quarkonium states: they are mesons made of a heavy quark and antiquark (namely, charmonium and bottomonium). Exploration of these states through non-relativistic quantum chromodynamics (NRQCD) and lattice QCD are increasingly important tests of quantum chromodynamics.

Understanding bound states of hadrons such as pionium and protonium is also important in order to clarify notions related to exotic hadrons such as mesonic molecules and pentaquark states.

Footnotes

^ "Muonium" is the name assigned by IUPAC to an electron–antimuon bound state before the current convention became popular. So, despite its name, muonium is not a bound muon–antimuon onium. A muon–antimuon bound state is called "true muonium" to reduce confusion.

References

^ Walker, D.C. (1983). Muon and Muonium Chemistry. Cambridge University Press. p. 5. ISBN 978-0-521-24241-7. Retrieved 23 June 2020.
^ Labelle, P.; Zebarjad, S.M.; Burgess, C.P. (1997). "Nonrelativistic QED and next-to-leading hyperfine splitting in positronium". Physical Review D. 56 (12): 8053–8061. arXiv:hep-ph/9706449. Bibcode:1997PhRvD..56.8053L. doi:10.1103/PhysRevD.56.8053. S2CID 6258393.

[2] "Muonium" is the name assigned by IUPAC to an electron–antimuon bound state before the current convention became popular. So, despite its name, muonium is not a bound muon–antimuon onium. A muon–antimuon bound state is called "true muonium" to reduce confusion.

[1] Walker, D.C. (1983). Muon and Muonium Chemistry. Cambridge University Press. p. 5. ISBN 978-0-521-24241-7. Retrieved 23 June 2020.

[3] Labelle, P.; Zebarjad, S.M.; Burgess, C.P. (1997). "Nonrelativistic QED and next-to-leading hyperfine splitting in positronium". Physical Review D. 56 (12): 8053–8061. arXiv:hep-ph/9706449. Bibcode:1997PhRvD..56.8053L. doi:10.1103/PhysRevD.56.8053. S2CID 6258393.

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+{{Short description|Quantum state of a particle and its antiparticle}}
-{{Distinguish2|[[onium compounds]], ions such as ammonium}}
+{{Distinguish|text=[[onium ion]]s such as ammonium}}
-{{Unreferenced|date=October 2008}}
+{{Antimatter}}
-The suffix '''-onium''' (plural: '''onia''') refers to the bound state of a particle and its antiparticle. They are usually named by adding the suffix ''-onium'' to the name of the constituting particle. However, despite its name, [[Muonium]] is not a muon–antimuon onium because IUPAC assigned the name to the system of an antimuon bound with an electron. (Muon–antimuon onium would be named [[muononium]].)
+[[File:Structure of Protonium.svg|thumb|An illustration of the [[protonium]] atom.]]
+An '''onium''' (plural: '''onia''') is a [[bound state]] of a [[particle]] and its [[antiparticle]].<ref>{{cite book |last=Walker |first=D.C. |title=Muon and Muonium Chemistry |date=1983 |publisher=[[Cambridge University Press]] |isbn=978-0-521-24241-7 |page=5 |url=https://books.google.com/books?id=PM88AAAAIAAJ&pg=PA5-IA8 |access-date=23 June 2020 |language=en}}</ref> These states are usually named by adding the suffix ''-onium'' to the name of one of the constituent particles (replacing an ''-on'' suffix when present), with one exception for "[[muonium]]"; a  muon–antimuon bound pair is called "[[true muonium]]" to avoid confusion with old nomenclature.{{efn|"[[Muonium]]" is the name assigned by [[IUPAC]] to an [[electron]]–[[antimuon]] bound state before the current convention became popular. So, despite its name, [[muonium]] is not a bound muon–antimuon onium. A muon–antimuon bound state is called "[[true muonium]]" to reduce confusion.}}
 ==Examples==
-[[Positronium]] is an onium which consists of an [[electron]] and a [[positron]] bound together as a long-lived [[metastable]] state. Positronium has been studied since the 1950s to understand bound states in [[quantum field theory]]. A recent development called non-relativistic [[quantum electrodynamics]] (NRQED) used this system as a proving ground.
+[[Positronium]] is an onium which consists of an [[electron]] and a [[positron]] bound together as a long-lived [[metastable]] state. Positronium has been studied since the 1950s to understand bound states in [[quantum field theory]]. A recent development called [[non-relativistic quantum electrodynamics]] (NRQED) used this system as a proving ground.<ref>{{cite journal |last1=Labelle |first1=P. |last2=Zebarjad |first2=S.M. |last3=Burgess |first3=C.P. |year=1997 |title=Nonrelativistic QED and next-to-leading hyperfine splitting in positronium |journal=Physical Review D |volume=56 |issue=12 |pages=8053–8061 |bibcode=1997PhRvD..56.8053L |arxiv=hep-ph/9706449 |doi=10.1103/PhysRevD.56.8053 |s2cid=6258393 }}</ref>
-[[Pionium]], a bound state of two oppositely-charged [[pion]]s, is interesting for exploring the [[strong interaction]]. This should also be true of [[protonium]]. The true analogs of positronium in the theory of strong interactions, however, are not exotic atoms but certain [[meson]]s, the ''[[quarkonium]] states'', which are made of a heavy quark such as the [[charm quark|charm]] or [[bottom quark]] and its antiquark. ([[Top quark]]s are so heavy that they decay through the [[weak force]] before they can form bound states.) Exploration of these states through non-relativistic [[quantum chromodynamics]] (NRQCD) and [[lattice QCD]] are increasingly important tests of [[quantum chromodynamics]].
+[[Pionium]], a bound state of two oppositely-charged [[pion]]s, is interesting for exploring the [[strong interaction]]. This should also be true of [[protonium]]. The true analogs of positronium in the theory of strong interactions are the [[quarkonium]] states: they are [[meson]]s made of a heavy quark and antiquark (namely, charmonium and bottomonium). Exploration of these states through [[non-relativistic quantum chromodynamics]] (NRQCD) and [[lattice QCD]] are increasingly important tests of [[quantum chromodynamics]].
 Understanding bound states of [[hadron]]s such as [[pionium]] and [[protonium]] is also important in order to clarify notions related to [[exotic hadron]]s such as [[mesonic molecule]]s and [[pentaquark]] states.
 ==See also==
-{{wiktionary}}
+{{Wiktionary}}
-* [[Exotic atom]]
+*[[Exotic atom]]
+*[[Exciton]] — solid-state analog of positronium
+==Footnotes==
-{{Particles}}
+{{notelist}}
+==References==
-[[Category:Particle physics]]
+{{reflist}}
-[[Category:Onium|*]]
-{{Particle-stub}}
+{{Particles}}
-{{Quantum-stub}}
-[[it:Onio (fisica)]]
+[[Category:Onia| ]]
+[[Category:Particle physics]]
-[[ja:オニウム]]