Contents

Onium

Antimatter
Antiparticles Positron Antiproton Antineutron Antihydrogen Antihelium Onia Antiprotonic hydrogen Antiprotonic helium Muonium True muonium Pionium Positronium Quarkonium
Concepts and phenomena Annihilation Baryogenesis Baryon asymmetry Comet CP violation Gravitational interaction Positron emission
Devices Cloud chamber Particle accelerator Antiproton decelerator Relativistic Heavy Ion Collider Penning trap
Uses Positron emission tomography Fuel Weapon
People and bodies Carl David Anderson Paul Dirac Andrei Sakharov CERN
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Anonium (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]

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.

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• Exotic atom