First measurement of the K ± → π 0 π 0 μ ± ν decay

Abstract

Abstract The first observation of the decay K ± → π 0 π 0 μ ± v ( K μ 4 00 ) by the NA48/2 experiment at the CERN-SPS is reported. From 2437 selected signal candidates with 15% background contamination, the branching ratio of the decay is measured in the restricted kinematical space of the squared dilepton mass above 0.03 GeV2/c 4 and extrapolated to the full kinematical space. The result is found to be in agreement with the R form factor from 1-loop Chiral Perturbation Theory.