Study of the process $e^+e^- \to \pi^+\pi^-$ in the energy region 400<\sqrt[]{s}<1000 MeV

The cross section of the process e + e − → π + π − was measured in the SND experiment at the VEPP-2M collider in the energy region 400 < √ s < 1000 MeV. This measurement was based on about 12 . 4 × 10 6 selected collinear events, which include 7 . 4 × 10 6 e + e − → e + e − , 4 . 5 × 10 6 e + e − → π + π − and 0 . 5 × 10 6 e + e − → µ + µ − selected events. The systematic uncertainty of the cross section determination is 1.3 %. The ρ -meson parameters were determined: m ρ = 774 . 9 ± 0 . 4 ± 0 . 5 MeV, Γ ρ = 146 . 5 ± 0 . 8 ± 1 . 5 MeV, σ ( ρ → π + π − ) = 1220 ± 7 ± 16 nb as well as the parameters of the G -parity suppressed decay ω → π + π − : σ ( ω → π + π − ) = 29 . 9 ± 1 . 4 ± 1 . 0 nb and φ ρω = 113 . 5 ± 1 . 3 ± 1 . 7 degree.