Muon

Unstable elementary subatomic particle similar to electron but 207 times heavier.

Core Principles & Analysis

• Discovered in cosmic rays by Carl Anderson and Seth Neddermeyer in 1936.
• Decays with a mean lifetime of 2.2 microseconds; time dilation lets cosmic-ray muons reach sea level.
• Fermilab's Muon g−2 experiment measured its magnetic anomaly to 127 parts per billion in 2025.

Specifications & Metrics

• MASS: 105.6583755 ± 2.3 × 10⁻⁶ MeV/c²
• SPIN: 1/2
• SYMBOL: μ⁻
• MEAN LIFE: 2.1969811 × 10⁻⁶ ± 2.2 × 10⁻¹² s
• PDG ID: S004
• PDG EDITION: PDG 2026
• CHARGE: −1 e

Principal Decay Modes

• mu- → e- nubar_e nu_mu — ~100%
• mu- → e- nubar_e nu_mu gamma — 0.0000060 ± 0.0000005%
• mu- → e- nubar_e nu_mu e+ e- — 0.0034 ± 0.0004%

Branching fractions: Particle Data Group, 2026 edition (CC BY 4.0).

Open in the Simulator — run this concept live