Measurement of the Vacuum Decay Rate of Orthopositronium

Abstract

Accepted without review at the request of Daniel Sinclair under policy announced 26 April 1976Orthopositronium ($o\ensuremath{-}\mathrm{Ps}$), formed on the cone of a channel electron multiplier by 400-eV positrons, is shown to diffuse quickly into an MgO-coated evacuated chamber with energies up to 0.8 \ifmmode\pm\else\textpm\fi{} 0.2 eV. The decay rate of $o\ensuremath{-}\mathrm{Ps}$ is measured to be 7.09 \ifmmode\pm\else\textpm\fi{} 0.02 ${\mathrm{\ensuremath{\mu}}\mathrm{sec}}^{\ensuremath{-}1}$, where the error is due principally to systematic effects. This result is interpreted to be the first direct measurement of the vacuum decay rate of the $o\ensuremath{-}\mathrm{Ps}$. It is in disagreement with the theoretical value of 7.242 \ifmmode\pm\else\textpm\fi{} 0.008 \ensuremath{\mu} ${\mathrm{sec}}^{\ensuremath{-}1}$ and previous experiments in gases as well.