On the Lifetime of the pi+pi- Atom
A. Gall (Bern University), J. Gasser (Bern University), V. E., Lyubovitskij (JINR, Dubna, Tomsk University), A. Rusetsky (Bern, University, JINR, Dubna, Tbilisi University)
TL;DR
This paper derives a comprehensive formula for the decay width of the pi+pi- atom, incorporating QCD effects and isospin breaking, enabling precise extraction of pi-pi scattering lengths from lifetime measurements.
Contribution
It provides the first general expression for the pi+pi- atom decay width including leading and next-to-leading order isospin breaking effects.
Findings
Derived a formula for the decay width including QCD and photon effects.
Enables extraction of |a_0 - a_2| from experimental lifetime data.
Applicable to current and future pi+pi- atom lifetime measurements.
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 |a_0-a_2| 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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