New Experimental Value for the Orthopositronium Decay Rate

Abstract

The vacuum decay rate of orthopositronium formed in a gas is determined, after extrapolation to zero gas density, to be 7.056\ifmmode\pm\else\textpm\fi{}0.007 \ensuremath{\mu}${\mathrm{sec}}^{\ensuremath{-}1}$. The discovery of two systematic effects in a previous powder experiment is discussed. A new measurement of the decay rate in Si${\mathrm{O}}_{2}$ powders yields results in agreement with the new gas value. The experimental values are still in disagreement with the most recent theoretical calculation, 7.0386\ifmmode\pm\else\textpm\fi{}0.000 16 \ensuremath{\mu}${\mathrm{sec}}^{\ensuremath{-}1}$.