The goal of the DIRAC experiment at CERN is to measure with high precision
the lifetime of the π+π− atom (A2π), which is of order
3×10−15 s, and thus to determine the s-wave ππ-scattering
lengths difference ∣a0−a2∣. A2π atoms are detected through the
characteristic features of π+π− pairs from the atom break-up
(ionization) in the target. We report on a first high statistics atomic data
sample obtained from p Ni interactions at 24 GeV/c proton momentum and
present the methods to separate the signal from the background.Comment: 19 pages, 12 figures, 1 tabl