Observation of positronium annihilation in the 2S state: towards a new measurement of the 1S-2S transition frequency

TL;DR

This paper reports the first observation of positronium annihilation from the 2S state, using a novel detection method, paving the way for high-precision measurements of the 1S-2S transition frequency.

Contribution

It introduces a new method to detect laser-excited positronium in the 2S state through delayed annihilation photons, enabling more precise spectroscopic measurements.

Findings

First observation of positronium annihilation from the 2S state

Demonstration of a new detection method using delayed annihilation photons

Increased lifetime of positronium in the 2S state by a factor of eight

Abstract

We report the first observation of the annihilation of positronium from the 2S state. Positronium (Ps) is excited with a two-photon transition from the 1S to the 2S state where its lifetime is increased by a factor of eight compared to the ground state due to the decrease in the overlap of the positron electron wavefunction. The yield of delayed annihilation photons detected as a function of laser frequency is used as a new method of detecting laser-excited Ps in the 2S state. This can be considered the first step towards a new high precision measurement of the 1S-2S Ps line.