Explore the vast range of titles available.

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 recent precise measurements of the e+e− → K+K− and e+e− → KSKL cross sections and the hadronic spectral function of the τ− → K−KSντ decay are used to extract the isoscalar and isovector electromagnetic kaon form factors and their relative phase in a model independent way. The experimental results are compared with a fit based on the vector-meson-dominance model.

The SND is a non-magnetic detector deployed at the VEPP-2000 e + e − collider (BINP, Novosibirsk) for hadronic cross-section measurements in the center of mass energy range below 2 GeV. The important part of the detector is a hodoscopic electromagnetic calorimeter (EMC) with three layers of NaI(Tl) counters. EMC signal shaping and digitizing electronics based on FADC allow us to obtain both the energy deposition and the signal arrival time. We demonstrate how EMC time is applied to detect background pileup and cosmic events.

The process e+e-→ηηγ is studied in the center-of-mass energy range 1.17–2.00 GeV using data with an integrated luminosity of 201 pb-1 collected by the SND detector at the VEPP-2000 e+e- collider. The e+e-→ηηγ cross section is measured for the first time. It is shown that the dominant mechanism of this reaction is the transition through the ϕη intermediate state. Our result on the e+e-→ηηγ cross section is consistent with the e+e-→ϕη measurement in the ϕ→K+K- mode. The search for radiative processes contributing to the e+e-→ηηγ cross section is performed, and no significant signal is observed.

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.

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 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.

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.

The Spherical Neutral Detector (SND) is an experiment for e+e− annihilation study at low energies 0.2−2 GeV. The light quark anti−quark bound states are the main subject of study at these energies. They express themselves as resonances in the e+e− hadronic cross sections. Hadronic cross sections could be recalculated to hadronic vacuum polarization (HVP). The Standard Model predictions today are limited by HVP which is not calculable with modern QCD theory. In this talk we present the review of the hadronic cross sections measurements at SND and new measurements: e+e− → π+π−, π0γ, π+π−π0, ωπ0, K+K−η, η, KsKLπ0, π+π−π0η, ωπ0η e.t.c.