Muon magnetic moment to nuclear magneton ratio

$μ_μ/μ_N$ = −8.890 597 04(20)

Value: −8.890 597 04
Standard uncertainty: 2 × 10⁻⁷
Relative uncertainty: 2.2 × 10⁻⁸ (22 parts per billion)
Status: Measured
Symbol: $μ_μ/μ_N$
Source: CODATA 2022 via NIST · NIST entry

Use in a calculation

# muon magnetic moment to nuclear magneton ratio, CODATA 2022 (NIST)
muon_magnetic_moment_to_nuclear_magneton = -8.89059704  # standard uncertainty 2e-7

# SciPy: scipy.constants.physical_constants['muon mag. mom. to nuclear magneton ratio']

What it is

The magnetic moment of the muon, an unstable heavier cousin of the electron (about 207 times its mass) that lives about 2.2 microseconds, expressed in nuclear magnetons.

How the value changed, 1998–2022

Each point is one CODATA adjustment, plotted as its difference from the 2022 value; the bars show one standard uncertainty (an arrowhead means the bar runs off the chart).

Relative uncertainty

CODATA	Value (uncertainty)	Relative uncertainty	Change from previous
2022	−8.890 597 04(20)	2.2 × 10⁻⁸	−0.1 σ of 2018
2018	−8.890 597 03(20)	2.2 × 10⁻⁸	+0.1 σ of 2014
2014	−8.890 597 05(20)	2.2 × 10⁻⁸	−0.4 σ of 2010
2010	−8.890 596 97(22)	2.5 × 10⁻⁸	+0.3 σ of 2006
2006	−8.890 597 05(23)	2.6 × 10⁻⁸	−0.3 σ of 2002
2002	−8.890 596 98(23)	2.6 × 10⁻⁸	+2.7 σ of 1998
1998	−8.890 597 70(27)	3.0 × 10⁻⁸

“Change from previous” is the shift in the value divided by the standard uncertainty of the previous adjustment. Earlier values are converted into the current unit where NIST changed it (for example J s to J Hz⁻¹).