New Precision Measurements of the Decay Rates of Singlet and Triplet Positronium

Abstract

Both the singlet and triplet decay rates (${\ensuremath{\lambda}}_{S}, {\ensuremath{\lambda}}_{T}$) of positronium have been measured in a new direct timing experiment based on singlet-triplet state mixing for positronium formed in isobutane gas in a magnetic field. ${\ensuremath{\lambda}}_{S}=7.994\ifmmode\pm\else\textpm\fi{}0.011$ ${\mathrm{nsec}}^{\ensuremath{-}1}$ was found, a factor of 10 improvement in accuracy and the first measurement sensitive enough to test the radiative corrections to ${\ensuremath{\lambda}}_{S}$. ${\ensuremath{\lambda}}_{T}=7.051\ifmmode\pm\else\textpm\fi{}0.005$ \ensuremath{\mu}${\mathrm{sec}}^{\ensuremath{-}1}$ was found, in agreement with previous measurements. The combined ${\ensuremath{\lambda}}_{T}$ data are not in satisfactory agreement with theory.