The DIRAC experiment, a magnetic double arm spectrometer, aims to measure
the lifetime of [pi^{+}pi^{-}] atoms in the ground-state
with 10% precision, using the high energy and high intensity proton beam
of the CERN Proton Synchrotron. Since the value of the above lifetime of
order 1 fs is dictated by strong interaction at low energy, a precise measurement
of this quantity enables to determine the s-wave pion scattering lengths
to 5%. Already ten years ago, pion scattering lengths were studied in the
framework of chiral perturbation theory and values predicted at the same
level have up to now never been confronted with accurate experimental data.
Such a measurement would submit the understanding of chiral symmetry breaking
of QCD to a crucial check.

DIRAC
Collaboration Frascati
DIRAC group Experimental
setup Preliminary
results

Updated by Paola Gianotti 15/10/2001