The NA48 experiment at the CERN SPS was originally designed and used for the precision measurement of direct CP violation in kaon decays. Moreover, a large number of measurements of rare kaon and hyperon decays have been carried out. All four analyses presented here are based on the same data sample, taken in September 1999 during a special run with pure K L beam. A simple minimum bias trigger was set up to accept only events with two charged tracks, adequate to collect semileptonic K L decays.

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... During two days of data taking about 80 million 2-track events were recorded. We measured the branching ratio R of the decay K L → π ± e ∓ ν relative to all charged K L decays with two tracks: R = 0.4978 ± 0.0035. From this we derived the K e3 branching fraction BR (K e3 ) = 0.4010 ± 0.0028 exp. ± 0.0035 norm. and extracted the CKM parameter |Vus| = 0.2187 ± 0.0016 exp. ± 0.0023 theo. . The uncertainty on |Vus| is dominated by the insufficient knowledge of the vector form factor f K 0 π − + . From a sample of 18977 reconstructed K 0 e3γ and 5.6 million K 0 e3 events we measured the relative branching ratio BR (K L → π ± e ∓ νγ/K L → π ± e ∓ ν) = (0.964 ± 0.008 +0.011 −0.009 ) %. The same K 0 e3 sample was used to measure the Dalitz plot density. A linear q 2 dependence of the vector form factor was found. There is no evidence for scalar or tensor couplings. Assuming pure vector coupling, the result for the slope parameter is λ + = 0.0288 ± 0.0004 stat. ± 0.0011 syst. . In a similar way the Dalitz plot density for K L → π ± µ ∓ ν e events is being studied. Based on 2.64 million reconstructed K 0 µ3 decays in data, we obtain the preliminary results λ + = 0.0260 ± 0.0007 stat. ± 0.0010 syst. and λ 0 = 0.0120 ± 0.0008 stat. ± 0.0015 syst. .