Improved Measurement of the<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:msup><mml:mi>K</mml:mi><mml:mo>+</mml:mo></mml:msup><mml:mo>→</mml:mo><mml:msup><mml:mi>π</mml:mi><mml:mo>+</mml:mo></mml:msup><mml:mi>ν</mml:mi><mml:mover accent="true"><mml:mi>ν</mml:mi><mml:mo>¯</mml:mo></mml:mover></mml:math>Branching Ratio

Abstract

An additional event near the upper kinematic limit for ${K}^{+}\ensuremath{\rightarrow}{\ensuremath{\pi}}^{+}\ensuremath{\nu}\overline{\ensuremath{\nu}}$ has been observed by experiment E949 at Brookhaven National Laboratory. Combining previously reported and new data, the branching ratio is $\mathcal{B}({K}^{+}\ensuremath{\rightarrow}{\ensuremath{\pi}}^{+}\ensuremath{\nu}\overline{\ensuremath{\nu}})=({1.47}_{\ensuremath{-}0.89}^{+1.30})\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}10}$ based on three events observed in the pion momentum region $211&lt;P&lt;229\text{ }\mathrm{M}\mathrm{e}\mathrm{V}/c$. At the measured central value of the branching ratio, the additional event had a signal-to-background ratio of 0.9.