Observation of the Decay K+ --> pi+ mu+ mu-

TL;DR

This paper reports the first observation of the rare decay K+ --> pi+ mu+ mu- and measures its branching ratio, providing experimental data to compare with theoretical predictions from chiral perturbation theory.

Contribution

The paper presents the first measurement of the decay K+ --> pi+ mu+ mu-, including its branching ratio, advancing experimental validation of theoretical models.

Findings

Measured branching ratio: (5.0 +/- 0.4 (stat.) +/- 0.7 (sys.) +/- 0.6 (theor.)) x 10^{-8}

Observed the rare decay K+ --> pi+ mu+ mu- for the first time

Results are compared with chiral perturbation theory predictions

Abstract

We have observed the rare decay K+ --> pi+ mu+ mu- and measured the branching ratio Gamma(K+ --> pi+ mu+ mu-)/Gamma(K+ --> all) = (5.0 +/- 0.4 (stat.) +/- 0.7 (sys.) +/- 0.6 (theor.)) x 10^{-8}. We compare this result with predictions from chiral perturbation theory and estimates based on the decay K+ --> pi+ e+ e-.