Precision measurement of the branching ratio K^{+}→π^{+}π^{0}/K^{+}→μ^{+}ν_{μ}

A measurement of the branching ratio K+-->pi+pi-0/K+-->mu+v(mu) was made using stopped kaons from ppBAR annihilations at rest and a magnetic spectrometer to measure the momenta of the charged decay product to the 1% to 1.5% level. The determination is based on 45 500 events passing final data cuts. The resulting ratio is 0. 3329+/-0.0047 (statistical) +/-0.0010 (systematic).