Producing long-lived 2 ~3S positronium via 3 ~3P laser excitation in magnetic and electric fields

摘要

Producing positronium (Ps) in the metastable 2 ~3S state is of interest for various applications in fundamental physics.We report here on an experiment in which Ps atoms are produced in this long-lived state by spontaneous radiative decay of Ps excited to the 3 3P level manifold. The Ps cloud excitation is obtained with a UV laser pulse in an experimental vacuum chamber in presence of guiding magnetic field of 25 mT and an average electric field of 300 V cm~(?1). The evidence of the 2 ~3S state production is obtained to the 3.6σ level of statistical significance using a novel analysis technique of the single-shot positronium annihilation lifetime spectra. The dynamic of the Ps population on the involved levels has been studied with a rate equation model.