Final state radiation and a possibility to test a pion-photon interaction model near two-pion threshold

TL;DR

This paper investigates final state radiation in electron-positron to pion pair processes, using Monte Carlo simulations to estimate non-pointlike pion effects and proposing a model-independent test for pion-photon interactions near the two-pion threshold.

Contribution

It introduces a Monte Carlo generator incorporating resonance effects and proposes a novel, model-independent method to test pion-photon interaction models.

Findings

Estimated non-pointlike pion effects using Resonance Perturbation Theory

Accounted for $$ meson intermediate states in simulations

Proposed a new method for model-independent testing of pion-photon interactions

Abstract

Final state radiation in the process $e^+e^-\to\pi^+\pi^-$ is considered for the cuts used in the analysis of KLOE data at large angles. By means of a Monte Carlo event generator FEVA, effects of non-pointlike behaviour of pions are estimated in the framework of Resonance Perturbation Theory. An additional complication related with the $\phi$ meson intermediate state is taken into account and the corresponding contributions (the direct decay $\phi\to\pi^+\pi^-\gamma$ and the double resonance decay $\phi\to\rho^\pm\pi^\mp\to\pi^+\pi^-\gamma$) are added to FEVA. A method to test effects of non-pointlike behaviour of pions in a model-independent way is proposed.