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RESEARCH PRODUCT

New results on kaon decays from NA48

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We report on recent results on rare and semileptonic kaon decays from NA48 and NA48/2. Using data from a minimum bias run in 1999 we present a new measurement of the CP violating decay K L → π + π − with over 40000 selected events. We measured the ratio Γ ( K L → π + π − ) / Γ ( K L → π ± e ∓ ν ) = ( 4.835 ± 0.038 ) × 10 −3 leading to the precise determination of the CP violation parameter | η + − | = ( 2.223 ± 0.013 ) × 10 −3 . From the same data we selected over 2 × 10 6 K L → π ± μ ∓ ν decays. Preliminary results from a dalitz plot fit yield the values for the form factors λ + = 0.0260 ± 0.0007 s t a t ± 0.0010 s y s t and λ 0 = 0.0120 ± 0.0008 s t a t ± 0.0015 s y s t . In one month of data taking in 2003 the NA48/2 experiment collected over 2 × 10 5 K ± → π ± π 0 γ decays. A measurement of the relative contributions of Inner Bremsstrahlung, Direct Emission, and their interference is presented which results in f r a c ( D E ) = ( 3.35 ± 0.35 s t a t ± 0.25 s y s t ) % and f r a c ( I N T ) = ( − 2.67 ± 0.81 s t a t ± 0.73 s y s t ) % showing for the first time a non-zero value of the interference term.