The negative positronium ion Ps − is a bound system consisting of two electrons and a positron. Its three constituents are pointlike leptonic particles of equal mass, which are subject only to the electroweak and gravitational force. Hence, Ps − is an ideal object in which to study the quantum mechanics of a three-body system. The ground state of Ps − is stable against dissociation but unstable against annihilation into photons. We report here on a precise measurement of the Ps − ground-state decay rate , which was carried out at the high-intensity NEutron induced POsitron source MUniCh (NEPOMUC) at the research reactor FRM II in Garching. A value of = 2.0875(50) ns −1 was obtained, which is three times more precise than previous experiments and in agreement with most recent theoretical predictions. The achieved experimental precision is at the level of the leading corrections in the theoretical predictions.

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Software-intensive systems are subject to continuous change due to modification of the systems themselves and their environment. Methods for supporting evolution are a competitive edge in software engineering as software is operated over decades. Empirical research is useful to validate the effectiveness of these methods. However, empirical studies on software evolution are rarely comprehensive and hardly replicable. Collaboration in empirical studies may prevent these shortcomings. We analyzed the support for such collaboration and examined existing studies in a literature review. Based on our findings, we designed CoCoMEP-a platform for supporting collaboration in empirical research on software evolution by shared knowledge. We report lessons learned from the application of the platform in a large research programme.

Methods for supporting evolution of software-intensive systems are a competitive edge in software engineering as software is often operated over decades. Empirical research is useful to validate the e®ectiveness of these methods. However, empirical studies on software evolution are rarely comprehensive and hardly replicable. Collaboration may prevent these shortcomings. We designed CoCoMEP À À À a platform for supporting collaboration in empirical research on software evolution by shared knowledge. We report lessons learned from the application of the platform in a large research programme.