Precise Measurement of the Pi+ -> Pi0 e+ nu Branching Ratio

TL;DR

This paper reports a highly precise measurement of the Pi+ -> Pi0 e+ nu decay branching ratio, confirming Standard Model predictions with improved accuracy using a calorimeter and stopped pion beam.

Contribution

The study provides the most precise experimental value of the Pi+ -> Pi0 e+ nu branching ratio, reducing uncertainties and validating theoretical predictions.

Findings

Measured branching ratio: (1.036 +/- 0.006) x 10^{-8}

Results agree with Standard Model predictions

Enhanced measurement precision over previous studies

Abstract

Using a large acceptance calorimeter and a stopped pion beam we have made a precise measurement of the rare Pi+ -> Pi0 e+ Nu,(pi_beta) decay branching ratio. We have evaluated the branching ratio by normalizing the number of observed pi_beta decays to the number of observed Pi+ -> e+ Nu, (pi_{e2}) decays. We find the value of Gamma(Pi+ -> Pi0 e+ Nu)/Gamma(total) = [1.036 +/- 0.004(stat.) +/- 0.004(syst.) +/- 0.003(pi_{e2})] x 10^{-8}$, where the first uncertainty is statistical, the second systematic, and the third is the pi_{e2} branching ratio uncertainty. Our result agrees well with the Standard Model prediction.