$({\mathit m}_{{{\mathit e}^{+}}}–{\mathit m}_{{{\mathit e}^{-}}})/{\mathit m}_{\mathrm {average}}$

INSPIRE  
A test of $\mathit CPT$ invariance.
VALUE CL% DOCUMENT ID TECN  COMMENT
$\bf{<8 \times 10^{-9}}$ 90 1
FEE
1993
CNTR Positronium spectroscopy
• • We do not use the following data for averages, fits, limits, etc. • •
$<4 \times 10^{-23}$ 90 2
DOLGOV
2014
From photon mass limit
$<4 \times 10^{-8}$ 90
CHU
1984
CNTR Positronium spectroscopy
1  FEE 1993 value is obtained under the assumption that the positronium Rydberg constant is exactly half the hydrogen one.
2  DOLGOV 2014 result is obtained under the assumption that any mass difference between electron and positron would lead to a non-zero photon mass. The PDG 2012 limit of $1 \times 10^{-18}$ eV on the photon mass is in turn used to derive the value quoted here.
Conservation Laws:
$\mathit CPT$ INVARIANCE
References:
DOLGOV 2014
PL B732 244 A Cosmological Bound on ${{\mathit e}^{+}}{{\mathit e}^{-}}$ Mass Difference
FEE 1993
PR A48 192 Measurement of the Positronium 1${}^{3}S_{1}$ $−$ 2${}^{3}S_{1}$ Interval by Continuous-Wave Two-photon Excitation
CHU 1984
PRL 52 1689 Measurement of the Positronium 1${}^{3}S_{1}$ $−$ 2${}^{3}S_{1}$ Interval by Doppler Free Two Photon Spectroscopy