Rare decay \pi^0 \to e^+e^- as a Test of Standard Model

TL;DR

This paper reviews experimental and theoretical progress on the rare decay ^0 e^+e^- and discusses deviations from Standard Model predictions, including recent data, new estimates, and implications for related decays.

Contribution

It provides a comprehensive review of recent experimental data, theoretical estimates, and their implications for the Standard Model and related meson decays.

Findings

Experimental data shows a 3.3 sigma deviation from theory.

New model-independent estimate of decay branching.

Impact of BABAR data on pion decay predictions.

Abstract

Experimental and theoretical progress concerning the rare decay \pi^0 \to e^+e^- is briefly reviewed. It includes the latest data from KTeV and a new model independent estimate of the decay branching which show the deviation between experiment and theory at the level of $3.3\sigma$. The predictions for \eta and \eta' decays into lepton pair are presented. We also comment on the impact on the pion rare decay estimate of the BABAR collaboration on the pion transition form factor at large momentum transfer.