Fermi coupling constant
Atomic & nuclearMeasured
= 1.166 3787(6) × 10−5 GeV−2
- Value
- 1.166 3787 × 10−5 GeV−2
- Standard uncertainty
- 6 × 10−12 GeV−2
- Relative uncertainty
- 5.1 × 10−7 (514 parts per billion)
- Status
- Measured
- Symbol
- Source
- CODATA 2022 via NIST · NIST entry
Use in a calculation
# Fermi coupling constant, CODATA 2022 (NIST)
fermi_coupling_constant = 1.1663787e-5 # GeV^-2, standard uncertainty 6e-12
# SciPy: scipy.constants.physical_constants['Fermi coupling constant']What it is
Sets the strength of the weak interaction at low energies, the force behind beta decay. Its value comes mainly from the measured lifetime of the muon.
Equations
- muon decay rate (leading order)
In other units
| Unit | Value | |
|---|---|---|
| CGS (cm−4 g−2 s4) | 4.543 7957 |
Converted with ConstantID's unit table; digits are rounded to the precision of the value, and a long exact value is rounded only for display. The relative uncertainty is unchanged by conversion to an exactly defined unit.
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 | 1.166 3787(6) × 10−5 | 5.1 × 10−7 | +0.0 σ of 2018 |
| 2018 | 1.166 3787(6) × 10−5 | 5.1 × 10−7 | +0.0 σ of 2014 |
| 2014 | 1.166 3787(6) × 10−5 | 5.1 × 10−7 | +2.9 σ of 2010 |
| 2010 | 1.166 364(5) × 10−5 | 4.3 × 10−6 | −0.6 σ of 2006 |
| 2006 | 1.166 37(1) × 10−5 | 8.6 × 10−6 | −2.0 σ of 2002 |
| 2002 | 1.166 39(1) × 10−5 | 8.6 × 10−6 | +0.0 σ of 1998 |
| 1998 | 1.166 39(1) × 10−5 | 8.6 × 10−6 |
“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).