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A bstract The cross section of the process e + e − → π + π − has been measured in the Spherical Neutral Detector (SND) experiment at the VEPP-2000 e + e − collider VEPP-2000 in the energy region 525 < s < 883 MeV. The measurement is based on data with an integrated luminosity of about 4.6 pb − 1 . The systematic uncertainty of the cross section determination is 0.8% at s > 0 . 600 GeV. The ρ meson parameters are obtained as m ρ = 775 . 3 ± 0 . 5 ± 0 . 6 MeV, Γ ρ = 145 . 6 ± 0 . 6 ± 0 . 8 MeV, B ρ → e + e− × B ρ → π + π− = (4 . 89 ± 0 . 02 ± 0 . 04) × 10 − 5 , and the parameters of the e + e − → ω → π + π − process, suppressed by G -parity, as B ω → e + e− × B ω → π + π− = (1 . 32 ± 0 . 06 ± 0 . 02) × 10 − 6 and and ϕ ρω = 110 . 7 ± 1 . 5 ± 1 . 0 degrees.

The process e+e-→nn¯ is studied in the experiment at the VEPP-2000 e+e- collider with the SND detector. The technique of the time measurements in the multichannel NaI(Tl) electromagnetic calorimeter is used to select nn¯ events. The value of the measured cross section in the center-of-mass energy range from 1.894 to 2 GeV varies from 0.5 to 0.35 nb. The effective neutron timelike form factor is derived from the measured cross section and compared with the proton form factor. The ratio of the neutron electric and magnetic form factors is obtained from the analysis of the antineutron polar angle distribution and found to be consistent with unity.

We present the preliminary measurement of the two-photon η-meson production cross section: . The measurements were carried out by the SND detector at the VEPP-2000 collider in the energy range from 1 to 2 GeV, the integral luminosity of the order of 0.5 fb –1 was used. The η-meson was detected at the six-photon final state, without scattered electrons registration. From the cross section of this process, we extract the two-photon η-meson width. The experimental results obtained can be used to calculate the hadronic contribution to the light by light scattering and to interpret the results of the muon anomalous magnetic moment measurement’s and to calculate the electromagnetic interaction constant at Z boson mass scale.

Abstract The process $$e^+e^-\\rightarrow K^+K^-\\pi ^0$$ e + e - → K + K - π 0 is studied with the SND detector at the VEPP-2000 $$e^+e^-$$ e + e - collider. Basing on data with an integrated luminosity of 26.4  $$\\hbox {pb}^{-1}$$ pb - 1 we measure the $$e^+e^-\\rightarrow K^+K^-\\pi ^0$$ e + e - → K + K - π 0 cross section in the center-of-mass energy range from 1.28 up to 2 GeV. The measured mass spectrum of the $$K\\pi $$ K π system indicates that the dominant mechanism of this reaction is the transition through the $$K^{*}(892)K$$ K ∗ ( 892 ) K intermediate state. The cross section for the $$\\phi \\pi ^0$$ ϕ π 0 intermediate state is measured separately. The SND results are consistent with previous measurements in the BABAR experiment and have comparable accuracy. We study the effect of the interference between the $$\\phi \\pi ^0$$ ϕ π 0 and $$K^*K$$ K ∗ K amplitudes. It is found that the interference gives sizable contribution to the measured $$e^+e^- \\rightarrow \\phi \\pi ^0\\rightarrow K^+K^-\\pi ^0$$ e + e - → ϕ π 0 → K + K - π 0 cross section below 1.7 GeV.

Abstract The process $$e^+e^-\\rightarrow \\eta \\pi ^0\\gamma $$ e + e - → η π 0 γ is studied in the center-of-mass energy range 1.05–2.00 GeV using data with an integrated luminosity of 94.5 $$\\hbox {pb}^{-1}$$ pb - 1 collected by the SND detector at the VEPP-2000 $$e^{+}e^{-}$$ e + e - collider. The $$e^+e^-\\rightarrow \\eta \\pi ^0\\gamma $$ e + e - → η π 0 γ cross section is measured for the first time. It is shown that the dominant mechanism of this reaction is the transition through the $$\\omega \\eta $$ ω η intermediate state. The measured cross section of the subprocess $$e^+e^-\\rightarrow \\omega \\eta \\rightarrow \\eta \\pi ^0\\gamma $$ e + e - → ω η → η π 0 γ is consistent with previous measurements in the $$e^+e^-\\rightarrow \\pi ^+\\pi ^-\\pi ^0\\eta $$ e + e - → π + π - π 0 η mode. It is found, with a significance of $$5.6\\sigma $$ 5.6 σ , that the process $$e^+e^-\\rightarrow \\eta \\pi ^0\\gamma $$ e + e - → η π 0 γ is not completely described by hadronic vector-pseudoscalar intermediate states. The cross section of this missing contribution, which can originate from radiation processes, e. g. $$e^+e^-\\rightarrow a_{0}(1450)\\gamma $$ e + e - → a 0 ( 1450 ) γ , is measured. It is found to be 15–20 pb in the wide energy range from 1.3 to 1.9 GeV.

Abstract The dynamics of the process $$ e^+e^- \\rightarrow \\pi ^+\\pi ^-\\pi ^0 $$ e + e - → π + π - π 0 is studied in the energy region from 1.15 to 2.00 GeV using data accumulated with the SND detector at the VEPP-2000 $$e^+e^-$$ e + e - collider. The Dalitz plot distribution and $$\\pi ^+\\pi ^-$$ π + π - mass spectrum are analyzed in a model including the intermediate states $$\\rho (770)\\pi $$ ρ ( 770 ) π , $$\\rho (1450)\\pi $$ ρ ( 1450 ) π , and $$\\omega \\pi ^0$$ ω π 0 . As a result, the energy dependences of the $$\\rho (770)\\pi $$ ρ ( 770 ) π and $$\\rho (1450)\\pi $$ ρ ( 1450 ) π cross sections and the relative phases between the $$\\rho (770)\\pi $$ ρ ( 770 ) π amplitude and the $$\\rho (1450)\\pi $$ ρ ( 1450 ) π and $$\\omega \\pi ^0$$ ω π 0 amplitudes are obtained. The $$\\rho (1450)\\pi $$ ρ ( 1450 ) π cross section has a peak in the energy region of the $$\\omega (1650)$$ ω ( 1650 ) resonance (1.55–1.75 GeV). In this energy range the contributions of the $$\\rho (770)\\pi $$ ρ ( 770 ) π and $$\\rho (1450)\\pi $$ ρ ( 1450 ) π states are of the same order of magnitude. No resonance structure near 1.65 GeV is observed in the $$\\rho (770)\\pi $$ ρ ( 770 ) π cross section. We conclude that the intermediate state $$\\rho (1450)\\pi $$ ρ ( 1450 ) π gives a significant contribution to the decay of $$\\omega (1650)\\rightarrow \\pi ^+\\pi ^-\\pi ^0$$ ω ( 1650 ) → π + π - π 0 , whereas the $$\\rho (770)\\pi $$ ρ ( 770 ) π mechanism dominates in the decay $$\\omega (1420)\\rightarrow \\pi ^+\\pi ^-\\pi ^0$$ ω ( 1420 ) → π + π - π 0 .

Abstract The cross section of the process e + e − → π + π − has been measured in the Spherical Neutral Detector (SND) experiment at the VEPP-2000 e + e − collider VEPP-2000 in the energy region 525 < s $$ \\sqrt{s} $$ < 883 MeV. The measurement is based on data with an integrated luminosity of about 4.6 pb −1. The systematic uncertainty of the cross section determination is 0.8% at s $$ \\sqrt{s} $$ > 0.600 GeV. The ρ meson parameters are obtained as m ρ = 775.3 ± 0.5 ± 0.6 MeV, Γ ρ = 145.6 ± 0.6 ± 0.8 MeV, B ρ→e+e− × B ρ→π+π− = (4.89 ± 0.02 ± 0.04) × 10 −5, and the parameters of the e + e − → ω → π + π − process, suppressed by G-parity, as B ω→e+e− × B ω→π+π− = (1.32 ± 0.06 ± 0.02) × 10 −6 and and ϕ ρω = 110.7 ± 1.5 ± 1.0 degrees.

Recent results of the SND detector experiments are presented. Data were taken at the VEPP-2000 and the VEPP-2M e+e− colliders in the Novosibirsk in the c.m. energy ranges from 0.3 to 2.00 GeV. Integrated luminosity used are 70pb-1 and 25pb-1 respectively. The cross sections of the e+e− → π0γ, K+K−, ωπ0, π+π−π0η, ωη, ωηπ0 processes has been measured.

New results on exclusive hadron production in e+e− annihilation obtained in experiments with the SND detector at the VEPP-2M and VEPP-2000 e+e− colliders are presented.

The reaction e+e−→ π+ π−π0η has been studied in the experiment with the SND detector at the VEPP-2000 e+ e− collider. The reaction proceeds via the four intermediate states: ωη, φη, a0ρ, and structureless π+π−π0η state, which may be, for example, ρ(1450) with ρ(1450) → ρ(770)η. The total e+e−→ π+π−π0η cross section and cross section for the four intermediate states have been measured and fitted in the vector meson dominance model.