Measurement of the decay rate of the negative ion of positronium (Ps-).

A new determination of the decay rate of the negative ion of positronium (Ps-), using a beam-foil method and a stripping-based detection technique, is reported. The measured result of gamma = 2.089(15) ns(-1) is a factor of 6 more precise than the previous experimental value of gamma = 2.09(9) ns(-1), and is in excellent agreement with the theoretical value of gamma = 2.086(6) ns(-1).