Study of the decay K+ => pi+,nu,nubar in the momentum region 140<Ppi<199 MeV/c

TL;DR

This paper reports the observation of seven K+ => pi+, nu, nubar decay events in a specific momentum range, providing a measurement of the decay's branching ratio and exploring implications for standard and alternative models.

Contribution

The study presents new experimental observations of rare kaon decays, increasing the known event count and refining the branching ratio measurement.

Findings

Observed seven decay events consistent with K+ => pi+, nu, nubar.

Measured branching ratio of approximately 1.73e-10.

Discussed implications for standard and alternative decay models.

Abstract

Experiment E949 at Brookhaven National Laboratory has observed three new events consistent with the decay K+ => pi+,nu,nubar in the pion momentum region 140 < P_pi < 199 MeV/c in an exposure of 1.71e12 stopped kaons with an estimated total background of 0.93+-0.17(stat.)+0.32-0.24(syst.) events. This brings the total number of observed K+ => pi+,nu,nubar events to seven. Combining this observation with previous results, assuming the pion spectrum predicted by the standard model, results in a branching ratio of (1.73+1.15-1.05)e-10. An interpretation of the results for alternative models of the decay K^ => pi+,nothing is also presented.