Measurements of Charged Kaon Semileptonic Decay Branching Fractions K^+- -> pi^0 mu^+- nu and K+- -> pi^0 e^+- nu and Their Ratio
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Measured ratios of decay rates for Ke3/K2π, K\mu3/K2πand K\mu3/Ke3 are presented. These measurements are based on K^+- decays collected in a dedicated run in 2003 by the NA48/2 experiment at CERN. The results obtained are Ke3/K2π= 0.2470 +/- 0.0009 (stat) +/- 0.0004 (syst) and K\mu3/K2π= 0.1637 +/- 0.0006 (stat) +/- 0.0003 (syst). Using the PDG average for the K^+- -> π^+-π^0 normalisation mode, both values are found to be larger than the current values given by the Particle Data Book and lead to a larger magnitude of the |V_{us}| CKM element than previously accepted. When combined with the latest Particle Data Book value of |V_{ud}|, the result is in agreement with unitarity of the CKM matrix. In addition, a new measured value of K\mu3/Ke3 = 0.663 +/- 0.003(stat) +/- 0.001(syst) is compared to the semi-empirical predictions based on the latest form factor measurements.
20 pages, 5 tables, 10 figures. Published in European Physical Journal C 50 2 (2007), contains erratum submitted to European Physical Journal C
20 pages, 5 tables, 10 figures. Published in European Physical Journal C 50 2 (2007), contains erratum submitted to European Physical Journal C