Measurement of the absolute branching ratio of the K+→π+π0(γ) decay with the KLOE detector

We have measured the absolute branching ratio of the K+→π+π0(γ) decay, using ∼20 million tagged K+ mesons collected with the KLOE detector at DAΦNE, the Frascati ϕ-factory. Signal counts are obtained from the fit of the distribution of the momentum of the charged decay particle in the kaon rest frame. The result, inclusive of final-state radiation, is BR(K+→π+π0(γ))=0.2065±0.0005stat±0.0008syst.