Determination of $\pi\pi$ scattering lengths from measurement of $\pi^+\pi^-$ atom lifetime

摘要

The DIRAC experiment at CERN has achieved a sizeable production of$\pi^+\pi^-$ atoms and has significantly improved the precision on its lifetimedetermination. From a sample of 21227 atomic pairs, a 4% measurement of theS-wave $\pi\pi$ scattering length difference $|a_0-a_2| =(.0.2533^{+0.0080}_{-0.0078}|_\mathrm{stat}.{}^{+0.0078}_{-0.0073}|_\mathrm{syst})M_{\pi^+}^{-1}$has been attained, providing an important test of Chiral Perturbation Theory.