New precision measurement of the orthopositronium decay rate: A discrepancy with theory

Abstract

The vacuum decay rate, ${\ensuremath{\lambda}}_{\mathrm{T}}$, of orthopositronium (o-Ps), formed in a gas, has been measured to be ${\ensuremath{\lambda}}_{\mathrm{T}}$=7.0516\ifmmode\pm\else\textpm\fi{}0.0013 \ensuremath{\mu}${\mathrm{s}}^{\mathrm{\ensuremath{-}}1}$. This result, which is 4 times more accurate than any previous measurement, is ten standard deviations above the theoretical value. Extensive systematic tests included measurement of ${\ensuremath{\lambda}}_{\mathrm{T}}$ in 3 different gases, each to an accuracy of at least \ifmmode\pm\else\textpm\fi{}0.0025 \ensuremath{\mu}${\mathrm{s}}^{\mathrm{\ensuremath{-}}1}$ (350 ppm), and the use of two entirely different digital timing systems.