Absolute Branching Ratio Normalization for Rare pi+ and mu+ Decays in the PIBETA Experiment

TL;DR

This paper reports precise measurements of rare pion and muon decays using the PIBETA detector, normalizing absolute branching ratios to independently measured decay counts, and discusses the consistency of the results.

Contribution

It provides new, precise absolute branching ratios for rare pi+ and mu+ decays, normalized to independently measured decay counts, enhancing the accuracy of weak decay data.

Findings

Measured absolute branching ratios for five rare decay modes.

Achieved high statistical precision with large data samples.

Confirmed mutual consistency of the preliminary results.

Abstract

We have used the PIBETA detector at the PSI for a precise measurement of rare pion and muon weak decays. We have collected a large statistical sample of (1) pi+ -> e+ nu, (2) pi+ -> pi0 e+ nu, (3) pi+ -> e+ nu gamma, (4) mu+ -> e+ nu nu, and (5) mu+ -> e+ nu nu gamma decays. We have evaluated the absolute branching ratios for these processes by normalizing to the independently measured number of decaying pi+'s (or mu+'s). We discuss the mutual consistency of the preliminary results.