title: Resolution of the orthopositronium-lifetime puzzle.
abstract: The long-standing discrepancy [G. S. Adkins, R. N. Fell, and J. Sapirstein, Ann. Phys. (N.Y.) 295, 136 (2002)]] between the theoretical calculations of the orthopositronium (o-Ps) annihilation decay rate (lambda(T)=1/lifetime) and some of the experimental measurements has been resolved. A focused beam of positrons incident on a special nanoporous silica film produces near-thermal energy o-Ps in vacuum that is slow enough to be virtually free of perturbing interactions. The fitted decay rate requires only a 500 ppm correction for nonthermal o-Ps effects. The new value of lambda(T)=7.0404(10)(8) micros(-1) is in excellent agreement with theory.
authors.affiliation: Randall Laboratory of Physics, University of Michigan, Ann Arbor, Michigan 48109-1120, USA. vallery@umich.edu
authors.forename: R S
authors.initials: RS
authors.lastname: Vallery
authors.forename: P W
authors.initials: PW
authors.lastname: Zitzewitz
authors.forename: D W
authors.initials: DW
authors.lastname: Gidley