Branching ratio of K0S decays into π+π- and π0π0 modes

We have measured the branching ratio R=Γ(K⁰_S-->π⁺π^-)Γ(K⁰_S-->π⁰π⁰) of K⁰_S produced in the reaction π^-+p-->Λ⁰+K⁰ in the 1.45 GeV / c π^- beam of the Princeton-Pennsylvania Accelerator. The K⁰_S decay secondaries were detected in an array of magnetostrictive-readout wire spark chambers interleaved with lead and copper radiators to convert γ rays. The position of K⁰ production in the target was detected with a unique trigger-target apparatus allowing a correction for the background produced by K⁰_L decays. The branching ratio corrected for this background and other standard effects is R=2.11+/-0.09, in good agreement with the world average.