A measurement of the K+ → e+v)(K+ → μ+v) branching ratio

The branching ratio $\text{R =}\text{Γ(}\text{K}{}^{\mathrm{+}}\text{→}\text{e}{}^{\mathrm{+}}\text{v)}\text{Γ(}\text{K}{}^{\mathrm{+}}\text{→ μ}{}^{\mathrm{+}}\text{v)}$ has been measured on the basis of 534 observed K⁺ → e⁺v decays. The K⁺ decay at rest; the momenta of the e⁺ and μ⁺ are measured in a magnetic spectrometer using multiwire driftchambers, and the electrons are identified in a gas Cerenkov counter. The result is R = (2.37 ± 0.17_× 10^?5. The value predicted for pure axial-vector interaction and μ-e-universality is R = 2.57 × 10^?5.