Precise determination of the branching ratio of the neutral-pion Dalitz decay

TL;DR

This paper presents a highly precise measurement of the ratio of decay widths for the neutral pion's Dalitz decay to the two-photon decay, refining previous values significantly using advanced QED corrections and updated form-factor data.

Contribution

It provides a new, more accurate value for the decay ratio of the neutral pion, incorporating complete next-to-leading-order radiative corrections and current form-factor measurements.

Findings

New ratio R = 11.978(6)×10^{-3} with two orders of magnitude precision improvement.

Derived branching ratios: 98.8131(6)% for gamma gamma and 1.1836(6)% for e+e- gamma decays.

Enhanced theoretical and experimental consistency in neutral pion decay measurements.

Abstract

We provide a new value for the ratio $R={\Gamma(\pi^0\to e^+e^-\gamma(\gamma))}/{\Gamma(\pi^0\to\gamma\gamma)}=11.978(6)\times10^{-3}$, which is by two orders of magnitude more precise than the current Particle Data Group average. It is obtained using the complete set of the next-to-leading-order radiative corrections in the QED sector, and incorporates up-to-date values of the $\pi^0$-transition-form-factor slope. The ratio $R$ translates into the branching ratios of the two main $\pi^0$ decay modes: $\mathcal{B}(\pi^0\to\gamma\gamma)=98.8131(6)\,\%$ and $\mathcal{B}(\pi^0\to e^+e^-\gamma(\gamma))=1.1836(6)\,\%$.