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An onium (plural: onia) is a bound state of a particle and its antiparticle. They are usually named by adding the suffix -onium to the name of the constituting particle except for Muonium which, despite its name, not a bound muon–antimuon onium, but an electron–antimuon bound state, and whose name was assigned by IUPAC. A muon–antimuon onium would be named true muonium or muononium.^{[citation needed]}

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.

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.

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 [[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.
-[[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.

Revision as of 11:27, 3 May 2016

Examples

See also