Measurement of Charged Kaon Semileptonic Decay Branching Fraction K~? → e~? ν~-＿eπ～0 Using ISTRA+ Detector?

摘要

The ratio of branching fractions for K~? → e～?ν~-_eπ~0 and K~? → π~?π~0 decays has been measured using the ISTRA+ spectrometer. The result of our measurement is the following: R_(K_(e3)/K_(2π)) = 0.2423 ± 0.0015(stat.) ± 0.0037(syst.). Using the current PDG value for the K_(2π) branching fraction, this result leads to the measured K_(e3) branching fraction of Br(K_(e3)) = 0.0501 ± 0.0009 and to the value of |V_(us)|f_+(0) = 0.2115 ± 0.0021.