New, high statistics measurement of the K+ ->pi0 e+ neutrino (K+e3) branching ratio

AGS collected ≈ 70,000 K + e 3 events to measure the K + e 3 branching ratio relative to the K + → π + π 0 , K + → π 0 µ + ν , and K + → π + π 0 π 0 decays. The π 0 was detected using the e + e − pair from π 0 → e + e − γ decay and no photons were required. Using the Particle Data Group branching ratios [ 1] for the normalization decays we obtain BR ( K + e 3( γ ) ) = (5 . 13 ± 0 . 02 stat ± 0 . 09 sys ± 0 . 04 norm )%, where K + e 3( γ ) includes the effect of virtual and real photons. This result is ≈ 2 . 3 σ higher than the current Particle Data Group value. Implications for the V us element of the CKM matrix, and the matrix’s unitarity are discussed.