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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.

Recent results on e + e − annihilation to hadrons from SND experiment at VEPP-2000 collider are presented. Corresponding data set is about 200 pb −1 of integrated luminosity collected at the energy region below 2 GeV. The processes e + e − → π + π − , π 0 γ, ωπ 0 , π + π − π 0 , ηπ + π − π 0 , η , π + π − 4π 0 have been studied. Searches for e + e − annihilation to C -even resonances η and f 1(1285) were done.

The process [Formula omitted] is studied with the SND detector at the VEPP-2000 [Formula omitted] collider. Basing on data with an integrated luminosity of 26.4 [Formula omitted] we measure the [Formula omitted] cross section in the center-of-mass energy range from 1.28 up to 2 GeV. The measured mass spectrum of the [Formula omitted] system indicates that the dominant mechanism of this reaction is the transition through the [Formula omitted] intermediate state. The cross section for the [Formula omitted] 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 [Formula omitted] and [Formula omitted] amplitudes. It is found that the interference gives sizable contribution to the measured [Formula omitted] cross section below 1.7 GeV.

The process [Formula omitted] is studied in the center-of-mass energy range 1.05-2.00 GeV using data with an integrated luminosity of 94.5 [Formula omitted] collected by the SND detector at the VEPP-2000 [Formula omitted] collider. The [Formula omitted] cross section is measured for the first time. It is shown that the dominant mechanism of this reaction is the transition through the [Formula omitted] intermediate state. The measured cross section of the subprocess [Formula omitted] is consistent with previous measurements in the [Formula omitted] mode. It is found, with a significance of [Formula omitted], that the process [Formula omitted] 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. [Formula omitted], is measured. It is found to be 15-20 pb in the wide energy range from 1.3 to 1.9 GeV.

The dynamics of the process [Formula omitted] is studied in the energy region from 1.15 to 2.00 GeV using data accumulated with the SND detector at the VEPP-2000 [Formula omitted] collider. The Dalitz plot distribution and [Formula omitted] mass spectrum are analyzed in a model including the intermediate states [Formula omitted], [Formula omitted], and [Formula omitted]. As a result, the energy dependences of the [Formula omitted] and [Formula omitted] cross sections and the relative phases between the [Formula omitted] amplitude and the [Formula omitted] and [Formula omitted] amplitudes are obtained. The [Formula omitted] cross section has a peak in the energy region of the [Formula omitted] resonance (1.55-1.75 GeV). In this energy range the contributions of the [Formula omitted] and [Formula omitted] states are of the same order of magnitude. No resonance structure near 1.65 GeV is observed in the [Formula omitted] cross section. We conclude that the intermediate state [Formula omitted] gives a significant contribution to the decay of [Formula omitted], whereas the [Formula omitted] mechanism dominates in the decay [Formula omitted].

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.

The process e+e-→ηπ0γ is studied in the center-of-mass energy range 1.05–2.00 GeV using data with an integrated luminosity of 94.5 pb-1 collected by the SND detector at the VEPP-2000 e+e- collider. The e+e-→ηπ0γ cross section is measured for the first time. It is shown that the dominant mechanism of this reaction is the transition through the ωη intermediate state. The measured cross section of the subprocess e+e-→ωη→ηπ0γ is consistent with previous measurements in the e+e-→π+π-π0η mode. It is found, with a significance of 5.6σ, that the process e+e-→ηπ0γ 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-→a0(1450)γ, is measured. It is found to be 15–20 pb in the wide energy range from 1.3 to 1.9 GeV.

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.

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.