New measurement of the K+ => pi+,nu,nubar branching ratio

TL;DR

This paper reports a new measurement of the rare K+ => pi+,nu,nubar decay, observing three events and estimating a branching ratio consistent with the standard model, refining previous results.

Contribution

It provides an improved measurement of the K+ => pi+,nu,nubar branching ratio based on new event observations and background estimation.

Findings

Observed three decay events in the specified pion momentum range.

Estimated background of approximately 0.93 events.

Measured branching ratio aligns with standard model predictions.

Abstract

Three events for the decay K+ => pi+,nu,nubar have been observed in the pion momentum region below the K+ => pi+,pi0 peak, 140 < P_pi < 199 MeV/c, with an estimated background of 0.93+-0.17(stat.)+0.32-0.24(syst.) events. Combining this observation with previously reported results yields a branching ratio of B(K+ => pi+,nu,nubar) = (1.73+1.15-1.05)e-10 consistent with the standard model prediction.