Study of the process $e^+e^- \to \pi^+\pi^-\pi^0$ in the energy region $\sqrt[]{s}$ below 0.98 GeV

TL;DR

This study measures the cross section of the $e^+e^- o ext{3 pions}$ process below 0.98 GeV, analyzes resonance parameters, and suggests evidence for suppressed $ ho$ decay into three pions.

Contribution

First precise measurement of the $e^+e^- o 3 ext{ pions}$ cross section below 0.98 GeV and analysis indicating possible $ ho$ decay into three pions.

Findings

Resonance parameters for the $ ho$, $ ho'$, and $ ho''$ mesons were determined.

Experimental data cannot be fully explained by known resonances alone.

Evidence suggests a suppressed $ ho o 3 ext{ pions}$ decay with a small branching ratio.

Abstract

The cross section of the process $e^+e^-\to \pi^+\pi^-\pi^0$ was measured in the Spherical Neutral Detector (SND) experiment at the VEPP-2M collider in the energy region $\sqrt[]{s}$ below 980 MeV. This measurement was based on about $1.2 \times 10^6$ selected events. The obtained cross section was analyzed together with the SND and DM2 data in the energy region $\sqrt[]{s}$ up to 2 GeV. The $\omega$-meson parameters: $m_\omega=782.79\pm 0.08\pm 0.09$ MeV, $\Gamma_\omega=8.68\pm 0.04\pm 0.15$ MeV and $\sigma(\omega\to 3\pi)=1615\pm 9\pm 57$ nb were obtained. It was found that the experimental data cannot be described by a sum of only $\omega$, $\phi$, $\omega^\prime$ and $\omega^{\prime\prime}$ resonances contributions. This can be interpreted as a manifestation of $\rho\to 3\pi$ decay, suppressed by $G$-parity, with relative probability $B(\rho\to 3\pi) = (1.01\pm^{0.54}_{0.36}\pm 0.034) \times 10^{-4}$.