Inparticle physics,true muonium is a theoretically predictedexotic atom representing a bound state of amuon and an antimuon (μ⁺μ⁻). The existence of true muonium is well established theoretically within theStandard Model. Its properties within the Standard Model are determined byquantum electrodynamics, and may be modified byphysics beyond the Standard Model.

True muonium is yet to be observed experimentally, though it may have been produced in experiments involving collisions ofelectron andpositron beams.^[1][2] The ortho-state of true muonium (i.e. the state with parallel alignment of the muon and antimuonspins) is expected to be relatively long-lived (with a lifetime of1.8×10⁻¹² s), and decay predominantly to an e⁺e⁻ pair, which makes it possible forLHCb experiment atCERN to observe it with the dataset collected by 2025.^[3]

There are several experimental projects searching for the true muonium.^[4] One of them is the μμ-tron experiment (Mumutron) planned at theBudker Institute of Nuclear Physics of theSiberian Branch of the Russian Academy of Sciences (INP SB RAS),^[5] which has been under development since 2017. The experiment involves the creation of a special low-energy electron–positroncollider, which will make it possible to observe the production of true muonium in collisions of electron and positron beams with an intersection angle of 75° with energies of 408 MeV. Thus, theinvariant mass of colliding particles will be equal to twice the mass of the muon (m_μ =105.658 MeV/c²). To register the exotic atom (in the decay channel into an electron–positron pair), it is planned to create a specialized detector. Apart to the actual detection of true muonium, it is planned to isolate its various states and measure their lifetimes.

In addition to experiments in the field of elementary particle physics, the collider created within the framework of the experiment is also of interest from the point of view of developing accelerator technologies for theSuper Charm-Tau factory planned at the INP SB RAS. The experiment was proposed in 2017 byE. B. Levichev [ru], A. I. Milshtein, andV. P. Druzhinin [ru], researchers at the INP SB RAS.

• Muonium
• Positronium
• Onium

• Low-energy electron-positron collider to search and study (μ⁺μ⁻) bound state. A.V. Bogomyagkov, V.P. Druzhinin, E.B. Levichev, A.I. Milstein, S.V. Sinyatkin. BINP, Novosibirsk.

Thisparticle physics–related article is astub. You can help Wikipedia byadding missing information.

• v
• t
• e

• Hypothetical composite particles
• Onia
• Particle physics stubs

• Articles with short description
• Short description is different from Wikidata
• All stub articles