Velocity-selected production of 2S3 metastable positronium

Abstract

Positronium in the 2 3 S metastable state exhibits a low electrical polarizability and a long lifetime (1140 ns) making it a promising candidate for interferometry experiments with a neutral matterantimatter system. In the present work, 2 3 S positronium is produced -in absence of electric field -via spontaneous radiative decay from the 3 3 P level populated with a 205 nm UV laser pulse. Thanks to the short temporal length of the pulse, 1.5 ns full-width at half maximum, different velocity populations of a positronium cloud emitted from a nanochannelled positron/positronium converter were selected by delaying the excitation pulse with respect to the production instant. 2 3 S positronium atoms with velocity tuned between 7 · 10 4 m s −1 and 10 · 10 4 m s −1 were thus produced. Depending on the selected velocity, a 2 3 S production efficiency ranging from ∼ 0.8% to ∼ 1.7%, with respect to the total amount of emitted positronium, was obtained. The observed results give a branching ratio for the 3 3 P-2 3 S spontaneous decay of (9.7 ± 2.7)%. The present velocity selection technique could allow to produce an almost monochromatic beam of ∼ 1 · 10 3 2 3 S atoms with a velocity spread < 10 4 m s −1 and an angular divergence of ∼ 50 mrad.

Techniques for Production and Detection of 23S Positronium

“…In the presence of are the areas below the spectra without and with the UV laser, respectively) and in the case of Fig. 2, it amounts to around 10%, between 500 and 800 ns from the prompt peak [16].…”

“…From the n = 3 level, Ps spontaneously decays to 2 3 S level (see Fig. 1) with a branching ratio of ≈ 10% [15,16]. The present experiments were performed by placing the e + /Ps converter in a 0.0250 T magnetic field.…”

“…SSPALS spectra were acquired and analyzed, with the procedure described in Refs. [15,16], with the goal to study the increase of the Ps lifetime due to the presence of atoms on the 2 3 S level.…”

“…In this work, an alternative way to produce 2 3 S Ps via the 3 3 P → 2 3 S spontaneous decay [15,16] is presented. We show that, with this method, it is possible to realize a monochromatic source of 2 3 S with tunable velocity and to form a monochromatic 2 3 S Ps beam [16]. Finally, a position-sensitive detector for a pulsed beam of Ps, with spatial resolution of around 90 µm [17], is described.…”

A ∼100 μm-resolution position-sensitive detector for slow positronium

“…For all the mentioned applications, it would be of great help to have a high spatial-resolution position sensitive detector for slow Ps. Indeed, it would allow monitoring the Ps emission from + e /Ps converters [12][13][14][15][16][17], it would be a quick diagnostic tool for Ps laser excitation experiments, it would permit the fast characterization in terms of transport and focus of a long-lived Ps beam [18][19][20] and, in the future, it could be employed in force-sensitive inertial experiments with Ps as test particle to detect and measure the fringe pattern generated by a deflectometer/interferometer device [11].…”