ConstantID

Tau mass energy equivalent

Atomic & nuclearMeasured

mτc2 = 2.846 84(19) × 10−10 J

Value
2.846 84 × 10−10 J
Standard uncertainty
1.9 × 10−14 J
Relative uncertainty
6.7 × 10−5 (67 parts per million)
Status
Measured
Symbol
mτc2
Source
CODATA 2022 via NIST · NIST entry

Use in a calculation

# tau mass energy equivalent, CODATA 2022 (NIST)
tau_mass_energy_equivalent = 2.84684e-10  # J, standard uncertainty 1.9e-14

# SciPy: scipy.constants.physical_constants['tau mass energy equivalent']

What it is

The rest energy (mass × c²) of the tau, the heaviest of the three charged leptons, in joules.

In other units

UnitValue
CGS (cm2 g s−2)0.002 846 84
keV kiloelectronvolt1 776 858
MeV megaelectronvolt1776.86
GeV gigaelectronvolt1.776 86
erg erg0.002 846 84

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).

tau mass energy equivalent: CODATA values 1998–2022 relative to the 2022 value, in parts per million, with one-standard-uncertainty bars−200−1000+100+200parts per million1998200220062010201420182022

Relative uncertainty

tau mass energy equivalent: relative standard uncertainty in each CODATA adjustment, logarithmic scale10⁻⁵10⁻⁴10⁻³1998200220062010201420182022
CODATAValue (uncertainty)Relative uncertaintyChange from previous
20222.846 84(19) × 10−106.7 × 10−5 +0.0 σ of 2018
20182.846 84(19) × 10−106.7 × 10−5 +0.2 σ of 2014
20142.846 78(26) × 10−109.1 × 10−5 +0.0 σ of 2010
20102.846 78(26) × 10−109.1 × 10−5 −0.6 σ of 2006
20062.847 05(46) × 10−101.6 × 10−4 +0.0 σ of 2002
20022.847 05(46) × 10−101.6 × 10−4 −0.2 σ of 1998
19982.847 15(46) × 10−101.6 × 10−4

“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 λ¯C,τ Reduced tau Compton wavelength 1.110 538(75) × 10−16 m Atomic & nuclear λC,τ Tau Compton wavelength 6.977 71(47) × 10−16 m Atomic & nuclear mτ/me Tau-electron mass ratio 3477.23(23) Atomic & nuclear mτc2 Tau energy equivalent 1776.86(12) MeV Atomic & nuclear mτ Tau mass 3.167 54(21) × 10−27 kg Atomic & nuclear mτ Tau mass in u 1.907 54(13) u Atomic & nuclear M(τ) Tau molar mass 1.907 54(13) × 10−3 kg mol−1 Atomic & nuclear mτ/mμ Tau-muon mass ratio 16.8170(11)