On the lifetime of the pi(+) pi(-) atom

The pi(+)pi(-) atom decays - in the ground state - predominantly into two n eutral pions. We present a general expression for the corresponding decay w idth in the framework of QCD (including photons). It contains all terms at leading and next-to-lending order in isospin breaking. The result allows on e to evaluate the combination \a(0) - a(2)\ of pi pi S-wave scattering leng ths from pi(+)pi(-) lifetime measurements, Like the one presently performed by the DIRAC experiment at CERN. (C) 1999 Published by Elsevier Science B. V. All lights reserved.