Improved Measurement of the K+ to pi+ nu nubar Branching Ratio

TL;DR

This paper reports an improved measurement of the rare decay K+ to pi+ nu nubar, combining new and previous data to refine the branching ratio estimate with three observed events near the kinematic limit.

Contribution

The study provides a more precise measurement of the K+ to pi+ nu nubar branching ratio by analyzing additional events from Experiment E949, enhancing previous results.

Findings

Branching ratio B(K+ to pi+ nu nubar) = 1.47 (+1.30, -0.89) x 10^-10

Three events observed in the pion momentum region 211<P<229 MeV/c

Signal-to-background ratio of 0.9 for the additional event

Abstract

An additional event near the upper kinematic limit for K+ to pi+ nu nubar has been observed by Experiment E949 at Brookhaven National Laboratory. Combining previously reported and new data, the branching ratio is B(K+ to pi+ nu nubar)= 1.47 (+1.30, - 0.89) x 10-10 based on three events observed in the pion momentum region 211<P<229 MeV/c. At the measured central value of the branching ratio, the additional event had a signal-to-background ratio of 0.9.