Measurement of the K+ -> pi0 mu+ nu_mu gamma Branching Ratio

TL;DR

This paper reports a measurement of the rare decay K+ -> pi0 mu+ nu_mu gamma, observing 40 events and determining its branching ratio, which aligns with theoretical expectations, using data from the E787 detector at Brookhaven.

Contribution

First measurement of the K+ -> pi0 mu+ nu_mu gamma decay branching ratio in a specific kinematic region with experimental data.

Findings

Branching ratio measured as (1.58 +- 0.46(stat.) +- 0.08(syst.)) x 10^{-5}.

Observed 40 events with an expected background of 16.5 events.

Results are consistent with theoretical predictions.

Abstract

A measurement of the decay K+ -> pi0 mu+ nu_mu gamma has been performed with the E787 detector at Brookhaven National Laboratory. Forty events were observed in the signal region with the background expectation of (16.5 +- 2.7) events. The branching ratio was measured to be (1.58 +- 0.46(stat.) +- 0.08(syst.)) x 10^{-5}} in the kinematic region Eg >30 MeV and theta_{mu gamma} > 20degree, where Eg is the energy of the emitted photon and theta_{mu gamma} is the angle between the muon and the photon in the K+ rest frame. The results were consistent with theoretical predictions.