Study of the process $e^+e^- \to \pi^+\pi^-\eta $ using initial state radiation

TL;DR

This study measures the cross section of the process $e^+e^- o \pi^+\pi^-\eta$ using initial state radiation data from BaBar, revealing resonance structures and observing $J/ ext{psi}$ decay events.

Contribution

First measurement of the $e^+e^- o \pi^+\pi^-\eta$ cross section in the 1.15-3.5 GeV range using initial state radiation data.

Findings

Cross section described by Vector-Meson Dominance model with four $ ho$-like states.

Observation of 49±9 $J/ ext{psi}$ decay events to $\pi^+\pi^-\eta$.

Measured product $\Gamma_{J/ ext{psi} o e^+e^-} ext{B}_{J/ ext{psi} o \pi^+\pi^-\eta} = 2.34 \\pm 0.43_{stat} \\pm 0.16_{syst}$ eV.

Abstract

We study the process $e^+e^- \to \pi^+\pi^-\eta \gamma$, where the photon is radiated from the initial state. About 8000 fully reconstructed events of this process are selected from the BaBar data sample with an integrated luminosity of 469~fb$^{-1}$. Using the $\pi^+\pi^-\eta$ invariant mass spectrum we measure the $e^+e^- \to \pi^+\pi^-\eta$ cross section in the $e^+e^-$ center-of-mass energy range from 1.15 to 3.5 GeV. The cross section is well described by the Vector-Meson Dominance model with four $\rho$-like states. We observe $49\pm9$ events of the $J/\psi$ decay to $\pi^+\pi^-\eta$, and measure the product $\Gamma_{J/\Psi \to e^+e^-} \text{B}_{J/\Psi \to \pi^+\pi^-\eta} = 2.34 \pm 0.43_{\text{stat}} \pm 0.16_{\text{syst}}$~eV.