Muon Mass Energy

The muon's rest energy, 105.658 MeV — 207 electron masses, and no one knows why.

Specifications & Metrics

symbol

mμc²

status

Measured — CODATA 2022 adjustment

value

105.6583755 ± 2.3 × 10⁻⁶ MeV

Relative Scale in Constants

Core Principles & Analysis

• The unexplained 206.77 ratio to the electron mass is the muon's original puzzle.
• Heavy enough to catalyse nuclear fusion; short-lived enough (2.2 μs) to make it hard.
• Its anomalous magnetic moment is the most precise Standard Model stress test running.