The muon is an elementary particle that is nearly identical to the electron in terms of electric charge (−1) and spin (½), but it is about 200 times more massive. Often described as a “heavier cousin” of the electron, the muon belongs to the lepton family in the Standard Model of particle physics.
Like the electron, the muon does not experience the strong nuclear force. It participates in:
- Electromagnetic interactions (because it has charge),
- Weak nuclear interactions (which allow it to decay), and
- Gravitational interactions (like all matter).
Key properties of the muon:
- Mass: Approximately 105.7 MeV/c² (compared to the electron’s 0.511 MeV/c²),
- Charge: −1 (same as the electron),
- Mean lifetime: Around 2.2 microseconds, after which it decays into an electron, a muon neutrino, and an electron antineutrino,
- Symbol: μ⁻ (for the negatively charged muon), with μ⁺ as its antiparticle.
Muons are naturally produced in cosmic ray interactions in Earth’s atmosphere and are also generated in particle accelerators. Despite their short lifetime, their high energy allows them to travel several kilometers through matter before decaying, which is why they can even be detected at the Earth’s surface.
Muons have important roles in:
- Probing materials via muon tomography (e.g., imaging volcanoes or ancient structures),
- Testing the Standard Model, especially in precision measurements like the muon g-2 experiment, which may hint at physics beyond the current theory.