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
Nearby in the stack
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.