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On the Lifetime of the pi+pi- Atom

A. Gall, J. Gasser, V. E. Lyubovitskij, A. Rusetsky

hep-pharXiv:hep-ph/9905309

Abstract

The pi+pi- atom decays -in the ground state - predominantly into two neutral pions. We present a general expression for the corresponding decay width in the framework of QCD (including photons). It contains all terms at leading and next-to-leading order in isospin breaking. The result allows one to evaluate the combination |a0-a2| of pi-pi S-wave scattering lengths from pi+pi- lifetime measurements, like the one presently performed by the DIRAC experiment at CERN.

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