Physicists at the University of Michigan have measured the lifetime of ‘orthopositronium’ with the highest precision yet. Positronium is like an ordinary hydrogen atom except that it has a positron and an electron bound together, instead of a proton and electron. This two-body system is unstable and has a very short lifetime, decaying in little over 100 nanoseconds. Until now, however, experiments had always measured lifetimes that did not agree with theory (R S Vallery et al. 2003 Phys. Rev. Lett. 90 203402).
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