Study of the $K^{\pm} \to \pi^{\pm}\pi^{0}e^{+}e^-$ decay by the NA48/2 experiment at CERN

The first observation of about 5000 candidates, with a 5% background contamination, of the rare decay K (±)→π (±) π (0) e (+) e (−) is reported by the NA48/2 experiment at CERN. From the analysis of 1.7 × 10(11) kaon decays collected in 2003-2004, the preliminary branching ratio in the full kinematic region is measured to be B(K → π (±) π (0) e (+) e(−) ) = (4.22 ± 0.15) × 10(−)(6). The observed value is in perfect agreement with theoretical predictions based on Chiral Perturbation Theory.