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

Producing positronium (Ps) in the metastable 2^3 S 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 3^3 P level manifold. The Ps cloud excitation is obtained with a UV laser pulse in an experimental vacuum chamber in presence of guiding magnetic eld of 25 mT and an average electric eld of 300 V cm^-1. The evidence of the 2^3 S state production is obtained to the 3.6 sigma level of statistical signicance 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.