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

  title={Observation of positronium annihilation in the 2S state: towards a new measurement of the 1S-2S transition frequency},
  author={David A. Cooke and P. Crivelli and Janis Alnis and Aldo Antognini and B. Brown and Susanne Friedreich and A. Gabard and Theodor W. Haensch and K. Kirch and Andr{\'e} Rubbia and Vjeran Vrankovic},
  journal={Hyperfine Interactions},
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 wave-function. 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… 

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