Study of isospin violating $\phi$ excitation in $e^+e^- \to \omega\pi^0$

TL;DR

This paper investigates the isospin-violating $ o$ $ ext{omega} ext{pi}^0$ reaction near the $ ext{phi}$ mass, analyzing mechanisms like electromagnetic transition, meson loops, and mixing, to understand the $ ext{phi}$ excitation and isospin violation effects.

Contribution

It introduces a comprehensive model combining electromagnetic and strong isospin violation mechanisms to analyze $ ext{phi}$ excitation in $e^+e^- o ext{omega} ext{pi}^0$, constrained by recent experimental data.

Findings

Extracted the $ ext{phi} o ext{omega} ext{pi}^0$ branching ratio from data.

Showed the branching ratio's sensitivity to the excitation line shape.

Provided insights into the link between isospin violation and OZI rule evasion.

Abstract

We study the reaction $e^+ e^-\to \omega\pi^0$ in the vicinity of $\phi$ mass region. The isospin-violating $\phi$ excitation is accounted for by two major mechanisms. One is electromagnetic (EM) transition and the other is strong isospin violations. For the latter, we consider contributions from the intermediate hadronic meson loops and $\phi$-$\rho^0$ mixing as the major mechanisms via the $t$ and s-channel transitions, respectively. By fitting the recent KLOE data, we succeed in constraining the model parameters and extracting the $\phi\to\omega\pi^0$ branching ratio. It shows that the branching ratio is sensitive to the $\phi$ excitation line shape and background contributions. Some crucial insights into the correlation between isospin violation and Okubo-Zweig-Iizuka (OZI) rule evading transitions are also learned.