ConstantID

Muon-electron mass ratio

Atomic & nuclearMeasured

mμ/me = 206.768 2827(46)

Value
206.768 2827
Standard uncertainty
4.6 × 10−6
Relative uncertainty
2.2 × 10−8 (22 parts per billion)
Status
Measured
Symbol
mμ/me
Source
CODATA 2022 via NIST · NIST entry

Use in a calculation

# muon-electron mass ratio, CODATA 2022 (NIST)
muon_electron_mass_ratio = 2.067682827e2  # standard uncertainty 4.6e-6

# SciPy: scipy.constants.physical_constants['muon-electron mass ratio']

What it is

The mass of the muon divided by the mass of the electron. Ratios like this are often measured more precisely than either quantity on its own, which is why CODATA lists them.

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).

muon-electron mass ratio: CODATA values 1998–2022 relative to the 2022 value, in parts per billion, with one-standard-uncertainty bars−150−100−500+50+100+150parts per billion1998200220062010201420182022

Relative uncertainty

muon-electron mass ratio: relative standard uncertainty in each CODATA adjustment, logarithmic scale10⁻⁹10⁻⁸10⁻⁷1998200220062010201420182022
CODATAValue (uncertainty)Relative uncertaintyChange from previous
2022206.768 2827(46)2.2 × 10−8 −0.1 σ of 2018
2018206.768 2830(46)2.2 × 10−8 +0.1 σ of 2014
2014206.768 2826(46)2.2 × 10−8 −0.3 σ of 2010
2010206.768 2843(52)2.5 × 10−8 +0.4 σ of 2006
2006206.768 2823(52)2.5 × 10−8 −0.3 σ of 2002
2002206.768 2838(54)2.6 × 10−8 +2.9 σ of 1998
1998206.768 2657(63)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).

Related constants

Atomic & nuclear λC,μ Muon Compton wavelength 1.173 444 110(26) × 10−14 m Atomic & nuclear gμ Muon g factor −2.002 331 841 23(82) Atomic & nuclear μμ Muon magnetic moment −4.490 448 30(10) × 10−26 J T−1 Atomic & nuclear aμ Muon g−2 1.165 920 62(41) × 10−3 Atomic & nuclear μμ/μB Muon magnetic moment to Bohr magneton ratio −4.841 970 48(11) × 10−3 Atomic & nuclear μμ/μN Muon magnetic moment to nuclear magneton ratio −8.890 597 04(20) Atomic & nuclear mμ Muon mass 1.883 531 627(42) × 10−28 kg Atomic & nuclear mμc2 Muon mass energy equivalent 1.692 833 804(38) × 10−11 J