On the Lifetime of the pi+pi- Atom
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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