Cross section of the reaction $e^+ e^- \to \pi^+\pi^-\pi^+\pi^- $ below 1 GeV at CMD-2

TL;DR

This study measures the cross section of the $e^+ e^- o ourpi$ process below 1 GeV, observing four-pion events at the $ ho$ meson energy for the first time, and estimates the $ ho^0$ decay width to four pions.

Contribution

First observation of four-pion events at the $ ho$ meson energy and measurement of the $ ho^0$ decay width to four pions at energies below 1 GeV.

Findings

Cross section agrees with $a_1(1260) o ourpi$ dominance above 1 GeV.

First detection of $ourpi$ events at the $ ho$ meson energy.

Estimated $ ho^0$ decay width to four pions: (2.8 ± 1.4 ± 0.5) keV.

Abstract

Using 3.07 ${pb}^{-1}$ of data collected in the energy range 0.60-0.97 GeV by CMD-2, about 150 events of the process $\epm \to \pch$ have been selected. The energy dependence of the cross section agrees with the assumption of the $a_1(1260) \pi$ intermediate state which is dominant above 1 GeV. For the first time \fourpi events are observed at the $\rho$ meson energy. Under the assumption that all these events come from the $\rho$ meson decay, the value of the cross section at the $\rho$ meson peak corresponds to the following decay width: \Gamma(\rho^0 \to \fourpi) = (2.8 \pm 1.4 \pm 0.5) {keV} or to the branching ratio B(\rho^0 \to \fourpi) = (1.8 \pm 0.9 \pm 0.3) \cdot 10 ^{-5}.