Precise measurement of the Decay K± ➞ π0 π0 µ± ν

Abstract

We report the first observation of the decay K ± → π 0 π 0 µ ± ν (K 00 µ4 ) by the NA48/2 experiment at the CERN SPS. From 2437 detected signal candidates with a S/B ratio of about 6, the branching ratio of the decay is determined with high precision. In the region of squared dilepton mass above 0.03 GeV 2 /c 4 , the branching ratio is found to be BR(K 00 µ4 , S l > 0.03) = (0.65 ± 0.03) × 10 −6 . The full phase space result BR(K 00 µ4 ) = (3.4 ± 0.2) × 10 −6 , depending on the decay model extrapolation, is in a reasonable agreement with the R form factor prediction from 1-loop Chiral Perturbation Theory.