A new decay rate measurement of the negative positronium ion

The results of a new decay rate measurement of the Ps- ion (e+e-e-) at the NEPOMUC high flux positron source (∼4.107 remoderated positrons per second) at the FRM II reactor in Garching are shown. The setup utilizes ∼5 nm thin Diamond Like Carbon (DLC) foils for the Ps- production as well as for stripping off the electrons, which takes place immediately after the acceleration across a variable length gap. This technique has been employed by a previous experiment in Heidelberg using a 22Na source resulting in the most recent decay rate value of Γ=2.089(15) ns-1. Higher statistics led to new insight into systematic errors, which could be improved by an electrically field-free decay gap, thus yielding an error of ∼0.2 %, which allows to test QED for this fundamental three-body system. In a further step the photodetachment cross section of Ps- will be measured at the two energies provided by the fundamental and second harmonic mode of a high power Nd:YAG laser for the first time.