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→\pch have been selected. The energy dependence of the cross section agrees with the assumption of the a1(1260)π intermediate state which is dominant above 1 GeV. For the first time \fourpi events are observed at the ρ meson energy. Under the assumption that all these events come from the ρ meson decay, the value of the cross section at the ρ 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}.
Cite
@article{arxiv.hep-ex/9912020,
title = {Cross section of the reaction $e^+ e^- \to \pi^+\pi^-\pi^+\pi^- $ below 1 GeV at CMD-2},
author = {2 collaboration},
journal= {arXiv preprint arXiv:hep-ex/9912020},
year = {2016}
}