Electroweak parameters of the z0 resonance and the standard model

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Observation of the decay K-S -> pi(+)pi(-)e(+)e(-)

We present the first observation of the decay KS → π+π-e+e- based upon the data collected in 1998 by the NA48 experiment at CERN. We have identified a clean sample of 56 events with negligible background contamination. Using KL → π+π-πD/0 decays as normalization sample, the branching ratio is measured to be BR(KS → π+π-e+e-) = [4,5 ± 0.7 (stat) ± 0.4(syst)] × 10-5. This result is in good agreement with the theoretical expectations from the mechanism of inner bremsstrahlung. © 2000 Elsevier Science B.V

Search for the decay K-S -> pi(0) gamma gamma

A search for the decay KS → π0γγ has been made using the NA48 detector at the CERN SPS. Using data collected in 1999 during a 40-hour run with a high-intensity KS beam, an upper limit for the branching ratio BR(KS → π0γγ, z ≥ 0.2) < 3.3 x 10-7 has been obtained at 90% confidence level, where z = m2γγ/mKO2. © 2003 Published by Elsevier Science B.V