Recent results on kaon decays by the NA48/2 experiment at CERN

The NA48/2 experiment reports the first observation of the rare decay K^± → π^±π⁰e⁺e^?, based on about 2000 candidates from 2003 data. The preliminary branching ratio in the full kinematic region is (mathcal {B}(K^{pm } to pi ^{pm }pi ^{0}e^{+}e^{-})=(4.06pm 0.17)cdot 10^{-6}). A sample of 4.687 × 10⁶(K^{pm }to pi ^{pm }{pi ^{0}_{D}}) events collected in 2003/4 is analyzed to search for the dark photon ((A^{prime })) via the decay chain K^± → π^±π⁰, (pi ^{0}to gamma A^{prime }), (A^{prime }to e^{+}e^{-}). No signal is observed, limits in the plane mixing parameter ε² versus its mass (m_{A^{prime }}) are reported.