No abstract

We present a measurement of the pion form factor based on e + e − annihilation data from the CMD-2 detector in the energy range 0.6 < √ s < 1.0 GeV with a systematic uncertainty of 0.8%. A data sample is five times larger than that used in our previous measurement.

The cross section of the process e + e − → π + π − has been measured using about 114000 events collected by the CMD-2 detector at the VEPP-2M e + e − collider in the center-of-mass energy range from 0.61 to 0.96 GeV. Results of the pion form factor determination with a 0.6% systematic uncertainty are presented. The following values of the ρ-and ω-meson parameters were found: M ρ = (776.09± 0.81) MeV, Γ ρ = (144.46 ± 1.55) MeV, Γ(ρ → e + e − ) = (6.86 ± 0.12) keV, Br(ω → π + π − ) = (1.33 ± 0.25)%. Implications for the hadronic contribution to the muon

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: mρ = 774.9 ± 0.4 ± 0.5 MeV, Γρ = 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 φρω = 113.5±1.3±1.7 degree.