Measurement of the annihilation decay rate of 2 ³S₁ positronium

Abstract

We report a measurement of the annihilation decay rate of 2 3 S1 positronium (Ps) atoms, Γexp(2 3 S1). Ground state atoms optically excited to radiatively metastable 2 3 S1 states were quenched via Stark mixing by the application of a time-delayed electric field. Rapid radiative decay of the Stark-mixed states to the ground state, followed by self-annihilation, was observed via the annihilation radiation time spectrum, and used to determine the number of excited state atoms remaining at different times, and hence the decay rate. We obtain Γexp(2 3 S1) = 843 ± 72 kHz, in broad agreement with the Zeeman-shifted theoretical value of 890 kHz.