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

Abstract

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

Comments: 6 pages, 6 figures