Tatyana Dimova

The corrected cross section of the e + e − → π+π− process measured in the spherical neutral detector experiment at the VEPP-2M e + e − collider is presented. The update is necessary due to a flaw in the e + e − → π+π− and e + e − → μ+μ− Monte Carlo event generators used previously in data analysis.

The process e+e−→n¯n has been studied at the VEPP-2000 e+e− collider with the SND detector in the energy range from threshold up to 2 GeV. As a result of the experiment, the e+e−→n¯n cross section and effective neutron form factor have been measured.3 MoreReceived 15 October 2014DOI:https://doi.org/10.1103/PhysRevD.90.112007© 2014 American Physical Society

The Spherical Neutral Detector (SND) operates at VEPP-2M collider in Novosibirsk studying e+e− annihilation in the energy range up to 1.4 GeV. Detector consists of a fine granulated spherical scintillation calorimeter with 1632 NaI(Tl) crystals, two cylindrical drift chambers with 10 layers of sense wires, and a muon system made of streamer tubes and plastic scintillation counters. The detector design, performance, data acquisition and processing are described.

In the SND experiment at VEPP-2M e+e− collider the φ(1020)→π0π0γ decay was studied and its branching ratio was measured: B(φ→π0π0γ)=(1.221±0.098±0.061)·10−4. It was shown, that f0(980)γ intermediate state dominates in this decay and the f0(980)-meson parameters were obtained.

The cross section of the process e + e − → π+π− was measured in the spherical neutral detector experiment at the VEPP-2M collider in the energy region $$400 < \sqrt s < 1000 MeV$$ . This measurement was based on about 12.4 × 106 selected collinear events, which include 7.4 × 106 e + e − → e + e −, 4.5 × 106 e + e − → π+π−, and 0.5 × 106 e + e − → μ+μ− selected events. The systematic uncertainty of cross section determination is 1.3%. The ρ-meson parameters were determined as m ρ = 774.9±0.4±0.5 MeV, Γ ρ = 146.5±0.8±1.5 MeV, and σ(ρ → π+π−) = 1220 ± 7 ± 16 nb and the parameters of the G-parity suppressed decay ω → π+π− as σ(ω → π+π−) = 29.9 ± 1.4 ± 1.0 nb and φρω = 113.5±1.3±1.7°.

The process ${e}^{+}{e}^{\ensuremath{-}}\ensuremath{\rightarrow}{\ensuremath{\pi}}^{0}\ensuremath{\gamma}$ is studied with the SND detector at the VEPP-2M ${e}^{+}{e}^{\ensuremath{-}}$ collider. The ${e}^{+}{e}^{\ensuremath{-}}\ensuremath{\rightarrow}{\ensuremath{\pi}}^{0}\ensuremath{\gamma}$ cross section is measured in the center-of-mass energy range from 0.60 to 1.38 GeV. The cross section is well described by the vector meson dominance model. From the fit to the cross-section data we determine the branching fractions $B(\ensuremath{\rho}\ensuremath{\rightarrow}{\ensuremath{\pi}}^{0}\ensuremath{\gamma})=(4.20\ifmmode\pm\else\textpm\fi{}0.52)\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}4}$, $B(\ensuremath{\omega}\ensuremath{\rightarrow}{\ensuremath{\pi}}^{0}\ensuremath{\gamma})=(8.88\ifmmode\pm\else\textpm\fi{}0.18)%$, and $B(\ensuremath{\phi}\ensuremath{\rightarrow}{\ensuremath{\pi}}^{0}\ensuremath{\gamma})=(1.367\ifmmode\pm\else\textpm\fi{}0.072)\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}3}$, and the relative phase between the $\ensuremath{\rho}$ and $\ensuremath{\omega}$ amplitudes ${\ensuremath{\varphi}}_{\ensuremath{\rho}}=(\ensuremath{-}12.7\ifmmode\pm\else\textpm\fi{}4.5)\ifmmode^\circ\else\textdegree\fi{}$. Our data on the process ${e}^{+}{e}^{\ensuremath{-}}\ensuremath{\rightarrow}{\ensuremath{\pi}}^{0}\ensuremath{\gamma}$ are the most accurate to date.

Rare radiative decay φ→ηπ0γ was studied with SND detector at VEPP-2M electron-positron collider and its branching ratio was measured: B(φ→ηπ0γ)=(0.88±0.14±0.09)·10−4. Significant contribution of the a0(980)γ intermediate state was observed in the decay. The result is based on total integrated luminosity corresponding to 2·107 produced φ mesons.

The cross sections of the processes e+e−→K+K−, e+e−→KSKL, and e+e−→π+π−π0 were measured in the SND experiment at the VEPP-2M collider in the energy region near the φ(1020) meson. These measurements were based on about 106 K+K−, 0.5×106 KSKL, and 0.4×106 π+π−π0 selected events. The measured cross sections have been analyzed in the framework of the vector meson dominance model and the main parameters of the φ resonance were obtained, such as its mass, width, the production cross section, and branching ratios of the main decay modes. The measured value of the φ meson total width, Γφ=4.21±0.04, is lower than the present world average of 4.458±0.032 MeV. Contributions in addition to the conventional vector meson dominance model were found in the e+e−→π+π−π0 reaction cross section.Received 15 September 2000DOI:https://doi.org/10.1103/PhysRevD.63.072002©2001 American Physical Society

In the SND experiment at VEPP-2M e+e− collider the φ(1020)→π0π0γ decay was studied. Its branching ratio B(φ→π0π0γ)=(1.14±0.10±0.12)·10−4 was measured. It was shown, that f0(980)γ mechanism dominates in this decay. Corresponding branching ratio B(φ→f0γ)=(3.42±0.30±0.36)·10−4 was obtained.

The cross section of the process ${e}^{+}{e}^{\ensuremath{-}}\ensuremath{\rightarrow}{\ensuremath{\pi}}^{+}{\ensuremath{\pi}}^{\ensuremath{-}}{\ensuremath{\pi}}^{0}$ was measured in the Spherical Neutral Detector (SND) experiment at the VEPP-2M collider in the energy region $\sqrt{s}$ below 980 MeV. This measurement was based on about $1.2\ifmmode\times\else\texttimes\fi{}{10}^{6}$ selected events. The obtained cross section was analyzed together with the SND and DM2 data in the energy region $\sqrt{s}$ up to 2 GeV. The $\ensuremath{\omega}$-meson parameters ${m}_{\ensuremath{\omega}}=782.79\ifmmode\pm\else\textpm\fi{}0.08\ifmmode\pm\else\textpm\fi{}0.09\mathrm{MeV},$ ${\ensuremath{\Gamma}}_{\ensuremath{\omega}}=8.68\ifmmode\pm\else\textpm\fi{}0.04\ifmmode\pm\else\textpm\fi{}0.15\mathrm{MeV},$ and $\ensuremath{\sigma}(\stackrel{\ensuremath{\rightarrow}}{\ensuremath{\omega}}3\ensuremath{\pi})=1615\ifmmode\pm\else\textpm\fi{}9\ifmmode\pm\else\textpm\fi{}57\mathrm{nb}$ were obtained. It was found that the experimental data cannot be described by a sum of only $\ensuremath{\omega},$ $\ensuremath{\varphi},$ ${\ensuremath{\omega}}^{\ensuremath{'}},$ and ${\ensuremath{\omega}}^{\ensuremath{''}}$ resonance contributions. This can be interpreted as a manifestation of $\stackrel{\ensuremath{\rightarrow}}{\ensuremath{\rho}}3\ensuremath{\pi}$ decay, suppressed by G parity, with a relative probability $B(\stackrel{\ensuremath{\rightarrow}}{\ensuremath{\rho}}3\ensuremath{\pi}{)=(1.01}_{\ensuremath{-}0.36}^{+0.54}\ifmmode\pm\else\textpm\fi{}0.034)\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}4}.$

Tracking system of the SND detector is fully assembled, equipped and tested with cosmic muons in 2007. During these tests operation conditions of the system were checked and optimized and main parameters of the system were measured. Design values of gas gain, detection efficiency and space resolution were achieved. Tracking system is ready for installation into the SND detector and coming data taking at the VEPP-2000 e+e--collider in Novosibirsk.

The cross section for the process e + e -→ ωπ 0 → π 0 π 0 γ has been measured in the center-of-mass energy range 1.05-2.00GeV.The experiment has been performed at the e + e -collider VEPP-2000 with the SND detector.The measured e + e -→ ωπ 0 cross section above 1.4 GeV is the most accurate to date.Below 1.4 GeV our data are in good agreement with the previous SND and CMD-2 measurements.Data on the e + e -→ ωπ 0 cross section are well described by the Vector Meson Dominance (VMD) model with two excited ρ-like states.From the measured cross section we have extracted the γ * → ωπ 0 transition form factor.It has been found that the VMD model cannot describe simultaneously our data and data obtained from the ω → π 0 µ + µ -decay.We have also tested Conserved Vector Current (CVC) hypothesis comparing our results on the e + e -→ ωπ 0 cross section with data on the τ -→ ωπ -ντ decay and have found that the CVC hypothesis works well within reached experimental accuracy of about 5%.

In the experiment with the SND detector at the VEPP-2000 ${e}^{+}{e}^{\ensuremath{-}}$ collider the cross section for the process ${e}^{+}{e}^{\ensuremath{-}}\ensuremath{\rightarrow}\ensuremath{\eta}{\ensuremath{\pi}}^{+}{\ensuremath{\pi}}^{\ensuremath{-}}$ has been measured in the center-of-mass energy range from 1.22 to 2.00 GeV. Obtained results are in agreement with previous measurements and have better accuracy. The energy dependence of the ${e}^{+}{e}^{\ensuremath{-}}\ensuremath{\rightarrow}\ensuremath{\eta}{\ensuremath{\pi}}^{+}{\ensuremath{\pi}}^{\ensuremath{-}}$ cross section has been fitted with the vector-meson dominance model. From this fit the product of the branching fractions $B(\ensuremath{\rho}(1450)\ensuremath{\rightarrow}\ensuremath{\eta}{\ensuremath{\pi}}^{+}{\ensuremath{\pi}}^{\ensuremath{-}})B(\ensuremath{\rho}(1450)\ensuremath{\rightarrow}{e}^{+}{e}^{\ensuremath{-}})$ has been extracted and compared with the same products for $\ensuremath{\rho}(1450)\ensuremath{\rightarrow}\ensuremath{\omega}{\ensuremath{\pi}}^{0}$ and $\ensuremath{\rho}(1450)\ensuremath{\rightarrow}{\ensuremath{\pi}}^{+}{\ensuremath{\pi}}^{\ensuremath{-}}$ decays. The obtained cross section data have been also used to test the conservation of vector current hypothesis.

We analyze a $37\text{ }\text{ }{\mathrm{pb}}^{\ensuremath{-}1}$ data sample collected with the SND detector at the VEPP-2000 ${e}^{+}{e}^{\ensuremath{-}}$ collider in the center-of-mass energy range 1.05--2.00 GeV and present an updated measurement of the ${e}^{+}{e}^{\ensuremath{-}}\ensuremath{\rightarrow}\ensuremath{\omega}{\ensuremath{\pi}}^{0}\ensuremath{\rightarrow}{\ensuremath{\pi}}^{0}{\ensuremath{\pi}}^{0}\ensuremath{\gamma}$ cross section. In particular, we correct the mistake in radiative correction calculation made in our previous measurement based on a part of the data. The measured cross section is fitted with the vector meson dominance model with three $\ensuremath{\rho}$-like states and used to test the conserved vector current hypothesis in the ${\ensuremath{\tau}}^{\ensuremath{-}}\ensuremath{\rightarrow}\ensuremath{\omega}{\ensuremath{\pi}}^{\ensuremath{-}}{\ensuremath{\nu}}_{\ensuremath{\tau}}$ decay.

The cross section of the e+e−→ωπ0→π0π0γ reaction was measured by the SND detector at VEPP-2M e+e− collider in the energy range from threshold up to 1.4 GeV. Results of the cross section fitting by the sum of ρ, ρ′ and ρ′′ contributions are presented.

The cross section of the process e+e−→π+π−π0 was measured in the Spherical Neutral Detector experiment at the VEPP-2M collider in the energy region s=980–1380 MeV. The measured cross section, together with the e+e−→π+π−π0 and ωπ+π− cross sections obtained in other experiments, was analyzed in the framework of the generalized vector meson dominance model. It was found that the experimental data can be described by a sum of ω, φ mesons and two ω′ and ω″ resonances contributions, with masses mω′∼1490, mω″∼1790 MeV and widths Γω′∼1210, Γω″∼560 MeV. The analysis of the π+π− invariant mass spectra in the energy region s from 1100 to 1380 MeV has shown that for their description one should take into account the e+e−→ωπ0→π+π−π0 mechanism also. The phase between the amplitudes corresponding to the e+e−→ωπ and e+e−→ρπ intermediate states was measured for the first time. The value of the phase is close to zero and depends on energy.Received 29 January 2002DOI:https://doi.org/10.1103/PhysRevD.66.032001©2002 American Physical Society

Signal of the rare radiative decay φ→ηπ0γ was observed in the SND experiment at VEPP-2M electron-positron collider. The result is based on the analysis of data, corresponding to a total integrated luminosity of 4pb−1, or 8·106 φ-mesons produced. The measured branching ratio of φ→ηπ0γ decay is equal to (0.83±0.23)·10−4.

The conversion decays φ→ηe+e− and η→γe+e− were studied by the SND detector using φ-meson production in e+e−-annihilation at VEPP-2M collider. The branching ratios of these decays were measured: Br(φ→ηe+e−)=(1.19±0.19±0.07)×10−4 and Br(η→γe+e−)=(5.15±0.62±0.39)×10−3. The e+e−-pair mass spectra and transition form factors were also studied.

Results of the study of the e+e−→π0γ process with SND detector at VEPP-2M collider in the c.m.s. energy range s=0.60–0.97 GeV are presented. Using 36513 selected events, corresponding to a total integrated luminosity of 3.4 pb−1, the e+e−→π0γ cross section was measured. The energy dependence of the cross section was analyzed in the framework of the vector meson dominance model. The data are well described by a sum of φ,ω,ρ→π0γ decay contributions with measured decay probabilities: Br(ω→π0γ)=(9.34±0.15±0.31)% and Br(ρ0→π0γ)=(5.15±1.16±0.73)×10−4. The ρ–ω relative interference phase is ϕρω=(−10.2±6.5±2.5) degrees.

The $e^+e^-\to K^+K^-$ cross section is measured in the center-of-mass energy range $1.05-2.00$ GeV at the SND detector. The measurement is based on data with an integrated luminosity of 35 pb$^{-1}$ collected at the VEPP-2000 $e^+e^-$-collider. The obtained results are consistent with the previous most accurate data obtained in the BABAR experiment and have a comparable accuracy.

The SND data acquisition system for experiments at VEPP-2000 collider is presented. Readout electronics, software architecture, key components are summarized. System was tested and used on the cosmics and VEPP-2000 collision events.

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 &lt; $$ \sqrt{s} $$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msqrt> <mml:mi>s</mml:mi> </mml:msqrt> </mml:math> &lt; 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 $$ \sqrt{s} $$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msqrt> <mml:mi>s</mml:mi> </mml:msqrt> </mml:math> &gt; 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.

Tungsten crystals oriented on their 〈111〉 axis, were submitted to 6 and 10 GeV electron beams on the SPS-CERN transfer lines. The crystals, 4 and 8 mm thick, used alone or associated to 4 mm thick amorphous disk, were studied as positron sources. The emerging positrons were detected by a Drift Chamber partially immersed in a magnetic field, where their trajectories were reconstructed providing the energy spectrum and the angular distribution. Significant enhancements were observed for the crystal source when compared to the amorphous one of the same thickness. The gain was larger than 3 and 2 for the 4 mm and 8 mm targets, respectively. The presented results look very promising for e+e− linear colliders.

In experiment with the SND detector at the VEPP-2M ${e}^{+}{e}^{\ensuremath{-}}$ collider the ${e}^{+}{e}^{\ensuremath{-}}\ensuremath{\rightarrow}\ensuremath{\eta}\ensuremath{\gamma}$ cross section was measured in the center-of-mass energy range $E=0.60--1.38\text{ }\text{ }\mathrm{GeV}$ with the integrated luminosity of $27.8\text{ }\text{ }{\mathrm{pb}}^{\ensuremath{-}1}$. The measured cross section is well described by the vector meson dominance model with contributions from the $\ensuremath{\rho}(770)$, $\ensuremath{\omega}(783)$, $\ensuremath{\phi}(1020)$, ${\ensuremath{\rho}}^{\ensuremath{'}}(1465)$ resonances and agrees with results of previous measurements. The decay probabilities $\mathcal{B}(\ensuremath{\phi}\ensuremath{\rightarrow}\ensuremath{\eta}\ensuremath{\gamma})$, $\mathcal{B}(\ensuremath{\omega}\ensuremath{\rightarrow}\ensuremath{\eta}\ensuremath{\gamma})$ and $\mathcal{B}(\ensuremath{\rho}\ensuremath{\rightarrow}\ensuremath{\eta}\ensuremath{\gamma})$ were measured with the accuracies better than or comparable to the world averages.

The cross section for the process $e^+e^- \to \omega\eta$ is measured in the center-of-mass energy range 1.34--2.00 GeV. The analysis is based on data collected with the SND detector at the VEPP-2000 $e^+e^-$ collider. The measured $e^+e^- \to \omega\eta$ cross section is the most accurate to date. A significant discrepancy is observed between our data and previous BABAR measurement.

The e+e−→π0π0γ process was studied in the SND experiment at VEPP-2M e+e− collider in the energy region 0.60–0.97 GeV. From the analysis of the energy dependence of measured cross section the branching ratios B(ω→π0π0γ)=(6.6+1.4−0.8±0.6)×10−5 and B(ρ→π0π0γ)=(4.1+1.0−0.9±0.3)×10−5 were obtained.

We present a measurement of the e + e − → K S K L cross section in the energy range √s = 1.04−1.38 GeV. For an energy of √s ≥ 1.2 GeV the cross section exceeds vector meson dominance model predictions with only ρ(770), ω(783), and ϕ(1020) mesons taken into account. The measured cross section agrees well with previous measurements.

The e+e−→ηγ cross section has been measured in the center-of-mass energy range 1.07–2.00 GeV using the decay mode η→3π0, π0→γγ. The analysis is based on 36 pb−1 of integrated luminosity collected with the SND detector at the VEPP-2000 e+e− collider. The measured cross section of about 40 pb at 1.5 GeV is explained by decays of the ρ(1450) and ϕ(1680) resonances.Received 29 December 2013DOI:https://doi.org/10.1103/PhysRevD.90.032002© 2014 American Physical Society

The ${e}^{+}{e}^{\ensuremath{-}}\ensuremath{\rightarrow}\ensuremath{\eta}{\ensuremath{\pi}}^{+}{\ensuremath{\pi}}^{\ensuremath{-}}$ cross section is measured at the Spherical Neutral Detector (SND) detector in the $\ensuremath{\eta}$ decay mode $\ensuremath{\eta}\ensuremath{\rightarrow}3{\ensuremath{\pi}}^{0}$. The analysis is based on the data sample with an integrated luminosity of $32.7\text{ }\text{ }{\mathrm{pb}}^{\ensuremath{-}1}$ collected at the VEPP-2000 ${e}^{+}{e}^{\ensuremath{-}}$ collider in the center-of-mass energy range $\sqrt{s}=1.075--2.000\text{ }\text{ }\mathrm{GeV}$. The data obtained in the $\ensuremath{\eta}\ensuremath{\rightarrow}3{\ensuremath{\pi}}^{0}$ decay mode are found to be in agreement with the previous SND measurements in the $\ensuremath{\eta}\ensuremath{\rightarrow}\ensuremath{\gamma}\ensuremath{\gamma}$ mode. Therefore the measurements in the two modes are combined.

The e+e−→ωπ0→π0π0γ process was investigated in the SND experiment at the VEPP-2M collider. A narrow energy interval near the φ-meson was scanned. The observed cross section reveals, at the level of three standard deviation, the interference effect caused by φ→π0π0γ decay. The cross-section parameters, as well as the real and imaginary parts of the φ-meson related amplitude, were measured.

A new kind of positron sources for future linear colliders, where the converter is an aligned tungsten crystal, oriented on the 〈1 1 1〉-axis, has been studied at CERN in the WA103 experiment with tertiary electron beams from the SPS. In such sources the photons resulting from channeling radiation and coherent bremsstrahlung create the e+e− pairs. Electron beams, of 6 and 10 GeV, were impinging on different kinds of targets: a 4 mm thick crystal, a 8 mm thick crystal and a compound target made of 4 mm crystal followed by 4 mm amorphous disk. An amorphous tungsten target 20 mm thick was also used for the sake of comparison with the 8 mm crystal and to check the ability of the detection system to provide the correct track reconstruction. The charged particles coming out from the target were detected in a drift chamber immersed partially in a magnetic field. The reconstruction of the particle trajectories provided the energy and angular spectrum of the positrons in a rather wide energy range (up to 150 MeV) and angular domain (up to 30°). The experimental approach presented in this article provides a full description of this kind of source. A presentation of the measured positron distribution in momentum space (longitudinal versus transverse) is given to allow an easy determination of the available yield for a given momentum acceptance. Results on photons, measured downstream of the positron detector, are also presented. A significant enhancement of photon and positron production is clearly observed. This enhancement, for a 10 GeV incident beam, is of 4 for the 4 mm thick crystal and larger than 2 for the 8 mm thick crystal. Another important result concerns the validation of the simulations for the crystals, for which a quite good agreement was met between the simulations and the experiment, for positrons as well as for photons. These results are presented after a short presentation of the experimental setup and of the track reconstruction procedure.

In the experiment with the SND detector at the VEPP-2M ${e}^{+}{e}^{\ensuremath{-}}$ collider measuring the ${e}^{+}{e}^{\ensuremath{-}}\ensuremath{\rightarrow}\ensuremath{\eta}\ensuremath{\gamma}$ cross section in the energy range $0.6&lt;\sqrt{s}&lt;1.38\text{ }\text{ }\mathrm{GeV}$ the reanalysis of data is performed. The goal is to improve the accuracy of the previous results by analyzing ambiguities in the approximation of energy dependence of the ${e}^{+}{e}^{\ensuremath{-}}\ensuremath{\rightarrow}\ensuremath{\eta}\ensuremath{\gamma}$ cross section, which were not taken into account in our previous study. We report new results on the approximation of the ${e}^{+}{e}^{\ensuremath{-}}\ensuremath{\rightarrow}\ensuremath{\eta}\ensuremath{\gamma}$ cross section based on the vector dominance model under new model parameter assumptions.

The cross section of the process ${e}^{+}{e}^{\ensuremath{-}}\ensuremath{\rightarrow}{K}^{+}{K}^{\ensuremath{-}}$ was measured in the energy range $\sqrt{s}=1.04--1.38\text{ }\text{ }\mathrm{GeV}$ in the SND experiment at the VEPP-2M ${e}^{+}{e}^{\ensuremath{-}}$ collider. The measured cross section is described by the model of vector meson dominance with contributions from the light vector mesons $\ensuremath{\rho}$, $\ensuremath{\omega}$, $\ensuremath{\phi}$ and their lowest excitations. The mean statistical accuracy of the measurement is 4.4%, and the systematic uncertainty is 5.2%.

A search for the process $e^+e^- \to \eta^\prime$ has been performed with the SND detector at the VEPP-2000 $e^+e^-$ collider. The data were accumulated at the center-of-mass energy of $957.78\pm 0.06$ MeV with an integrated luminosity of about 2.9 pb$^{-1}$. For reconstruction of the $\eta^\prime$ meson five decay chains have been used: $\eta^{\prime}\to\eta\pi^+\pi^-$ followed by the $\eta$ decays to $\gamma\gamma$ and $3\pi^0 $, and $\eta^{\prime} \to \eta\pi^0\pi^0$ followed by the $\eta$ decays to $\pi^+\pi^-\pi^0$, $\gamma\gamma$, and $3\pi^0$. As a result, the upper limit has been set on the $\eta^\prime$ electronic width: $\Gamma_{\eta^{\prime}\to e^+e^-} < 0.0020$ eV at the 90\% confidence level.

The process $e^+e^-\to\omega\eta\pi^0$ is studied in the energy range $1.45-2.00$ GeV using data with an integrated luminosity of 33 pb$^{-1}$ accumulated by the SND detector at the $e^+e^-$ collider VEPP-2000. The $e^+e^-\to\omega\eta\pi^0$ cross section is measured for the first time. The cross section has a threshold near 1.75 GeV. Its value is about 2 nb in the energy range $1.8-2.0$ GeV. The dominant intermediate state for the process $e^+e^- \to \omega\eta\pi^0$ is found to be $\omega a_0(980)$.

The $e^+e^- \rightarrow K_S K_L \pi^0$ cross section is measured in the center-of-mass energy range $\sqrt{s}=1.3-2.0$ GeV. The analysis is based on the data sample with an integrated luminosity of 33.5 pb$^{-1}$ collected with the SND detector at the VEPP-2000 $e^+e^-$ collider.

Abstract The process $$e^+e^-\rightarrow \eta \eta \gamma $$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mrow> <mml:msup> <mml:mi>e</mml:mi> <mml:mo>+</mml:mo> </mml:msup> <mml:msup> <mml:mi>e</mml:mi> <mml:mo>-</mml:mo> </mml:msup> <mml:mo>→</mml:mo> <mml:mi>η</mml:mi> <mml:mi>η</mml:mi> <mml:mi>γ</mml:mi> </mml:mrow> </mml:math> is studied in the center-of-mass energy range 1.17–2.00 GeV using data with an integrated luminosity of 201 pb $$^{-1}$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msup> <mml:mrow /> <mml:mrow> <mml:mo>-</mml:mo> <mml:mn>1</mml:mn> </mml:mrow> </mml:msup> </mml:math> collected by the SND detector at the VEPP-2000 $$e^+e^-$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mrow> <mml:msup> <mml:mi>e</mml:mi> <mml:mo>+</mml:mo> </mml:msup> <mml:msup> <mml:mi>e</mml:mi> <mml:mo>-</mml:mo> </mml:msup> </mml:mrow> </mml:math> collider. The $$e^+e^-\rightarrow \eta \eta \gamma $$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mrow> <mml:msup> <mml:mi>e</mml:mi> <mml:mo>+</mml:mo> </mml:msup> <mml:msup> <mml:mi>e</mml:mi> <mml:mo>-</mml:mo> </mml:msup> <mml:mo>→</mml:mo> <mml:mi>η</mml:mi> <mml:mi>η</mml:mi> <mml:mi>γ</mml:mi> </mml:mrow> </mml:math> cross section is measured for the first time. It is shown that the dominant mechanism of this reaction is the transition through the $$\phi \eta $$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mrow> <mml:mi>ϕ</mml:mi> <mml:mi>η</mml:mi> </mml:mrow> </mml:math> intermediate state. Our result on the $$e^+e^-\rightarrow \eta \eta \gamma $$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mrow> <mml:msup> <mml:mi>e</mml:mi> <mml:mo>+</mml:mo> </mml:msup> <mml:msup> <mml:mi>e</mml:mi> <mml:mo>-</mml:mo> </mml:msup> <mml:mo>→</mml:mo> <mml:mi>η</mml:mi> <mml:mi>η</mml:mi> <mml:mi>γ</mml:mi> </mml:mrow> </mml:math> cross section is consistent with the $$e^+e^-\rightarrow \phi \eta $$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mrow> <mml:msup> <mml:mi>e</mml:mi> <mml:mo>+</mml:mo> </mml:msup> <mml:msup> <mml:mi>e</mml:mi> <mml:mo>-</mml:mo> </mml:msup> <mml:mo>→</mml:mo> <mml:mi>ϕ</mml:mi> <mml:mi>η</mml:mi> </mml:mrow> </mml:math> measurement in the $$\phi \rightarrow K^+ K^-$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mrow> <mml:mi>ϕ</mml:mi> <mml:mo>→</mml:mo> <mml:msup> <mml:mi>K</mml:mi> <mml:mo>+</mml:mo> </mml:msup> <mml:msup> <mml:mi>K</mml:mi> <mml:mo>-</mml:mo> </mml:msup> </mml:mrow> </mml:math> mode. The search for radiative processes contributing to the $$e^+e^-\rightarrow \eta \eta \gamma $$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mrow> <mml:msup> <mml:mi>e</mml:mi> <mml:mo>+</mml:mo> </mml:msup> <mml:msup> <mml:mi>e</mml:mi> <mml:mo>-</mml:mo> </mml:msup> <mml:mo>→</mml:mo> <mml:mi>η</mml:mi> <mml:mi>η</mml:mi> <mml:mi>γ</mml:mi> </mml:mrow> </mml:math> cross section is performed, and no significant signal is observed.

The process $e^+e^- \to \pi^+\pi^-\pi^0\eta$ is studied in the center-of-mass energy region below 2 GeV with the SND detector at the VEPP-2000 $e^+e^-$ collider. The four intermediate states contribute to this process: $\omega\eta$, $\phi\eta$, $a_0(980)\rho$, and a structureless $\pi^+\pi^-\pi^0\eta$ state. We measure the total $e^+e^- \to \pi^+\pi^-\pi^0\eta$ cross section and the cross sections for its components: $\omega\eta$, $\phi\eta$, and a sum of $a_0(980)\rho$ and the structureless state. Our results are in agreement with previous measurements and have comparable or better accuracies.

In the experiment with the SND detector at VEPP-2M e+e− collider the process e+e−→π+π−π0 was studied in the energy range 2E0 from 1.04 to 1.38 GeV. A broad peak was observed with the visible mass Mvis=1220±20 MeV and cross section in the maximum σ0≃4 nb. The peak can be interpreted as a ω-like resonance ω(1200).

The invariant mass spectra of the π+π− and π±π0 pairs in the process e+e−→π+π−π0 were studied in the Spherical Neutral Detector experiment at the VEPP-2M collider in the energy region √s≃1020 MeV. These studies were based on about 0.5×106 events. The spectra were analyzed in the framework of the vector meson dominance model. It was found that the experimental data can be described assuming the e+e−→ρ→ππ+π−π0 transition only. An upper limit on the branching ratio of the φ(1020)→π+π−π0 decay through intermediate states different from ρπ was obtained at the 90% confidence level: B(→φπ+π−π0)<6×10−4. The ρ-meson mass and width which follow from the spectra analysis are mρ=775.0±1.3 MeV, Γρ=150.4±3.0 MeV. The mass difference of the neutral and charged ρ mesons was found to equal mρ±−mρ0=−1.3±2.3 MeV. In the π+π− mass spectrum the ρ−ω interference was seen at a two standard deviation level.Received 13 June 2001DOI:https://doi.org/10.1103/PhysRevD.65.032002©2002 American Physical Society

Axially oriented crystals, penetrated by high-energy electrons, are powerful photon sources and, hence, intense positron sources. Such kinds of positron sources have been studied experimentally at CERN, with the tertiary electron beam of the SPS having an energy of 6 and 10 GeV. Four and eight millimeters thick tungsten crystals and a compound target made of a 4 mm crystal followed by a 4 mm amorphous disk were used with an orientation along the 〈111〉 axis. The positrons were detected by a drift chamber, partially immersed in a magnetic field. The reconstructed trajectories allowed the determination of their energy and angular spectra. Significant enhancements were observed for the crystal source when compared to the amorphous one. The gain was about 3 for the 4 mm target and about 2 for the 8 mm and the compound targets. These preliminary results are described after short presentations of the experimental set-up and of the method of track reconstruction.

The search for lepton-flavor-violation process e^+e^-\to e\mu in the energy region \sqrt{s}=984 - 1060 MeV with SND detector at VEPP-2M e^+e^- collider is reported. The model independent 90% CL upper limits on the e^+e^-\to e\mu cross section, \sigma_{e\mu} < 11 pb, as well as on the corresponding \phi\to e\mu branching fraction, B(\phi\to e\mu) < 2 \times 10^{-6}, for the final particles polar angles 55^\circ<\theta<125^\circ, were obtained.

The process ${e}^{+}{e}^{\ensuremath{-}}\ensuremath{\rightarrow}{\ensuremath{\pi}}^{0}\ensuremath{\gamma}$ is studied with the SND detector at the VEPP-2000 ${e}^{+}{e}^{\ensuremath{-}}$ collider. Basing on data with an integrated luminosity of $41\text{ }\text{ }{\mathrm{pb}}^{\ensuremath{-}1}$ recorded in 2010-2012 we measure the ${e}^{+}{e}^{\ensuremath{-}}\ensuremath{\rightarrow}{\ensuremath{\pi}}^{0}\ensuremath{\gamma}$ cross section in the center-of-mass energy range from 1.075 up to 2 GeV. In the range 1.4--2.0 GeV the process ${e}^{+}{e}^{\ensuremath{-}}\ensuremath{\rightarrow}{\ensuremath{\pi}}^{0}\ensuremath{\gamma}$ is studied for the first time.

The reaction e+e−→ωπ0→π+π−π0π0 has been studied with SND detector at VEPP-2M e+e− collider in the vicinity of the φ meson resonance. The observed interference pattern in the energy dependence of the cross section is consistent with existence of the decay φ→ωπ0 with a branching ratio of B(φ→ωπ0)=(4.8+1.9−1.7±0.8)×10−5. The real and imaginary parts of the decay amplitude were measured. The φ→ωπ0 decay was observed for the first time.

Spherical Neutral Detector (SND) is a general purpose non-magnetic detector for experiments at VEPP-2000 e+e− collider in Novosibirsk in the energy range 2E=0.4–2.0GeV. Charged particle track coordinates are measured using drift and proportional chambers placed in a common gas volume. Particle identification is performed using energy deposition in the drift chamber at low particle momenta p⩽300MeV and aerogel threshold counters at high particle momenta p⩾300MeV. Photon energies are measured using 3-layer spherical electromagnetic calorimeter. Muons penetrating the detector and cosmic background muons are detected by the muon system based on proportional tubes and plastic scintillator counters. At present the detector is operating at VEPP-2000.

A search for direct production of the f1(1285) resonance in e+e− annihilation is performed with the SND detector at the VEPP-2000 e+e− collider. The analysis is based on data with an integrated luminosity of 15.1 pb−1 accumulated in the center-of-mass energy range 1.2–1.4 GeV. Two e+e−→f1(1285) candidate events are found at the peak of the resonance and zero events beyond the resonance. The significance of the e+e−→f1(1285) signal is 2.5σ. The cross section at the maximum of the resonance is found to be σ(e+e−→f1)=45−24+33 pb. The corresponding branching fraction B(f1(1285)→e+e−)=(5.1−2.7+3.7)×10−9. We consider this result as a first indication of the process e+e−→f1(1285). The measured branching fraction is consistent with the theoretical prediction.

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−→π+π− has been studied with the SND detector at VEPP-2M e+e− collider in the vicinity of φ(1020) resonance. From the analysis of the energy dependence of measured cross section the branching ratio B(φ→π+π−)=(7.1±1.1±0.9)·10−5 and the phase ψπ=−(34±4±3)° of interference with the non-resonant π+π− production amplitude were obtained.

The η→π0γγ decay was investigated by the SND detector at VEPP-2M e+e− collider in the reaction e+e−→φ→ηγ. Here we present the results and some details of this study. We report an upper limit (90% c.l.) Br(η→π0γγ)<8.4×10−4 as our final result. Our upper limit does not contradict the earlier measurement by GAMS spectrometer. To facilitate future studies a rather detailed review of the problem is also given.

Abstract The process $$e^+e^-\rightarrow \eta \pi ^0\gamma $$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mrow> <mml:msup> <mml:mi>e</mml:mi> <mml:mo>+</mml:mo> </mml:msup> <mml:msup> <mml:mi>e</mml:mi> <mml:mo>-</mml:mo> </mml:msup> <mml:mo>→</mml:mo> <mml:mi>η</mml:mi> <mml:msup> <mml:mi>π</mml:mi> <mml:mn>0</mml:mn> </mml:msup> <mml:mi>γ</mml:mi> </mml:mrow> </mml:math> is studied in the center-of-mass energy range 1.05–2.00 GeV using data with an integrated luminosity of 94.5 $$\hbox {pb}^{-1}$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msup> <mml:mtext>pb</mml:mtext> <mml:mrow> <mml:mo>-</mml:mo> <mml:mn>1</mml:mn> </mml:mrow> </mml:msup> </mml:math> collected by the SND detector at the VEPP-2000 $$e^{+}e^{-}$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mrow> <mml:msup> <mml:mi>e</mml:mi> <mml:mo>+</mml:mo> </mml:msup> <mml:msup> <mml:mi>e</mml:mi> <mml:mo>-</mml:mo> </mml:msup> </mml:mrow> </mml:math> collider. The $$e^+e^-\rightarrow \eta \pi ^0\gamma $$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mrow> <mml:msup> <mml:mi>e</mml:mi> <mml:mo>+</mml:mo> </mml:msup> <mml:msup> <mml:mi>e</mml:mi> <mml:mo>-</mml:mo> </mml:msup> <mml:mo>→</mml:mo> <mml:mi>η</mml:mi> <mml:msup> <mml:mi>π</mml:mi> <mml:mn>0</mml:mn> </mml:msup> <mml:mi>γ</mml:mi> </mml:mrow> </mml:math> cross section is measured for the first time. It is shown that the dominant mechanism of this reaction is the transition through the $$\omega \eta $$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mrow> <mml:mi>ω</mml:mi> <mml:mi>η</mml:mi> </mml:mrow> </mml:math> intermediate state. The measured cross section of the subprocess $$e^+e^-\rightarrow \omega \eta \rightarrow \eta \pi ^0\gamma $$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mrow> <mml:msup> <mml:mi>e</mml:mi> <mml:mo>+</mml:mo> </mml:msup> <mml:msup> <mml:mi>e</mml:mi> <mml:mo>-</mml:mo> </mml:msup> <mml:mo>→</mml:mo> <mml:mi>ω</mml:mi> <mml:mi>η</mml:mi> <mml:mo>→</mml:mo> <mml:mi>η</mml:mi> <mml:msup> <mml:mi>π</mml:mi> <mml:mn>0</mml:mn> </mml:msup> <mml:mi>γ</mml:mi> </mml:mrow> </mml:math> is consistent with previous measurements in the $$e^+e^-\rightarrow \pi ^+\pi ^-\pi ^0\eta $$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mrow> <mml:msup> <mml:mi>e</mml:mi> <mml:mo>+</mml:mo> </mml:msup> <mml:msup> <mml:mi>e</mml:mi> <mml:mo>-</mml:mo> </mml:msup> <mml:mo>→</mml:mo> <mml:msup> <mml:mi>π</mml:mi> <mml:mo>+</mml:mo> </mml:msup> <mml:msup> <mml:mi>π</mml:mi> <mml:mo>-</mml:mo> </mml:msup> <mml:msup> <mml:mi>π</mml:mi> <mml:mn>0</mml:mn> </mml:msup> <mml:mi>η</mml:mi> </mml:mrow> </mml:math> mode. It is found, with a significance of $$5.6\sigma $$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mrow> <mml:mn>5.6</mml:mn> <mml:mi>σ</mml:mi> </mml:mrow> </mml:math> , that the process $$e^+e^-\rightarrow \eta \pi ^0\gamma $$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mrow> <mml:msup> <mml:mi>e</mml:mi> <mml:mo>+</mml:mo> </mml:msup> <mml:msup> <mml:mi>e</mml:mi> <mml:mo>-</mml:mo> </mml:msup> <mml:mo>→</mml:mo> <mml:mi>η</mml:mi> <mml:msup> <mml:mi>π</mml:mi> <mml:mn>0</mml:mn> </mml:msup> <mml:mi>γ</mml:mi> </mml:mrow> </mml:math> 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. $$e^+e^-\rightarrow a_{0}(1450)\gamma $$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mrow> <mml:msup> <mml:mi>e</mml:mi> <mml:mo>+</mml:mo> </mml:msup> <mml:msup> <mml:mi>e</mml:mi> <mml:mo>-</mml:mo> </mml:msup> <mml:mo>→</mml:mo> <mml:msub> <mml:mi>a</mml:mi> <mml:mn>0</mml:mn> </mml:msub> <mml:mrow> <mml:mo>(</mml:mo> <mml:mn>1450</mml:mn> <mml:mo>)</mml:mo> </mml:mrow> <mml:mi>γ</mml:mi> </mml:mrow> </mml:math> , 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 $ e^+e^- \to \pi^+\pi^-\pi^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 $e^+e^-$ collider. The Dalitz plot distribution and $\pi^+\pi^-$ mass spectrum are analyzed in a model including the intermediate states $\rho(770)\pi$, $\rho(1450)\pi$, and $\omega\pi^0$. As a result, the energy dependences of the $\rho(770)\pi$ and $\rho(1450)\pi$ cross sections and the relative phases between the $\rho(770)\pi$ amplitude and the $\rho(1450)\pi $ and $\omega\pi^0$ amplitudes are obtained. The $\rho(1450)\pi$ cross section has a peak in the energy region of the $\omega(1650)$ resonance (1.55-1.75 GeV). In this energy range the contributions of the $\rho(770)\pi$ and $\rho(1450)\pi$ states are of the same order of magnitude. No resonance structure near 1.65 GeV is observed in the $\rho(770)\pi$ cross section. We conclude that the intermediate state $\rho(1450)\pi$ gives a significant contribution to the decay of $\omega (1650)\to\pi^+\pi^-\pi^0$, whereas the $\rho(770)\pi$ mechanism dominates in the decay $\omega(1420)\to\pi^+\pi^-\pi^0$.

Abstract Preliminary results of the first experiments at the new VEPP-2000 e + e − collider are presented. The experiments have been carried out in the center of mass energy range 1–2 GeV with instant luminosity 10 30 – 10 31 cm − 2 s − 1 and total integrated luminosity of about 10 pb − 1 . The main e + e − annihilation cross sections, π + π − π 0 π 0 , π + π − π 0 , π 0 π 0 γ , a n d π + π − η , have been measured. The cross section of nucleon–antinucleon production is also presented.

A search for the rare decay $\eta \rightarrow e^+e^-$ is performed using the inverse process $e^+e^- \rightarrow \eta$ in the decay mode $\eta\to\pi^0\pi^0\pi^0 $. We analyze data with an integrated luminosity of 654 nb$^{-1} $ accumulated at the VEPP-2000 $e^+e^-$ collider with the SND detector at the center-of-mass energy $E=m_\eta c ^2\approx 548 $ MeV, and set the upper limit $ {\cal B} (\eta \rightarrow e^+ e^-) < 7 \times 10^{-7} $ at the 90\% confidence level.

Two experiments, CMD-3 and SND, collected over 100 pb−1 in total taking data in 2011-2013 at the VEPP-2000 electron-positron collider. The data sample covers the whole available c.m. energy range from 0.32 GeV to 2.0 GeV. An upgrade of VEPP-2000 started in the second half of 2013, aimed at the luminosity increase up to 10 times at 2.0 GeV. Data taking is expected to resumed in 2015. The current results of analysis of the collected data for various modes of e+ e− → hadrons are discussed.

The preliminary results on multihadron processes obtained with the SND detector at the e + e − collider VEPP-2000 in the energy range from 1 to 2 GeV are presented. The results are interesting in connection with their contribution to the total hadronic cross section, the muon g-2 and a possibility to study excited vector mesons properties. The nucleon anti-nucleon production was also studied.

A sensitivity of the VEPP-2000 $e^+e^-$ collider in a search for the rare decay $\eta \rightarrow e^+ e^-$ has been studied. The inverse reaction $e^+ e^- \rightarrow \eta$ is proposed for this search. We have analyzed a data sample with an integrated luminosity of 108 nb$^{-1}$ collected with the SND detector in the center-of-mass energy range 520-580 MeV and found no background events for the reaction $e^+ e^- \rightarrow \eta$ in the decay mode $\eta\to\pi^0\pi^0\pi^0$. In the absence of background, a sensitivity to ${\cal B}(\eta \rightarrow e^+ e^-)$ of $10^{-6}$ can be reached during two weeks of VEPP-2000 operation. Such a sensitivity is better than the current upper limit on ${\cal B}(\eta \rightarrow e^+ e^-)$ by a factor of 2.3.

In the study of the reaction e+e−→ KSKL at the VEPP-2M e+e− collider with the SND detector the nuclear interaction length of KL meson in NaI(Tl) has been measured. Its value is found to be 30–50 cm in the KL momentum range 0.11–0.48 GeV/c. The results are compared with the values used in the simulation programs GEANT4 and UNIMOD.

The search for CP-violating KS→3π0 decay was performed with SND detector at VEPP-2M e+e− collider. The total amount of data corresponding to 7 million produced KS mesons was analyzed. No candidate events were found, giving an upper limit of the decay branching ratio: Br(KS→3π0)<1.4·10−5 at 90% confidence level.

The process e(+)e(-)-->mu(+)mu(-) has been studied by the SND detector at the VEPP-2M e(+)e(-) collider in the phi(1020)-resonance energy region. The measured effective phi meson leptonic branching ratio B(phi-->l(+)l(-)) identical with square root of B(phi-->e(+)e(-))B(phi-->mu(+)mu(-))] = (2.89 +/- 0.10 +/- 0.06) x 10(-4) agrees well with the Particle Data Group value B(phi-->e(+)e(-)) = (2.91 +/- 0.07) x 10(-4), confirming mu-e universality. Without additional assumption of mu-e universality the branching ratio B(phi-->mu(+)mu(-)) = (2.87 +/- 0.20 +/- 0.14) x 10(-4) was obtained.

Recent results from the SND detector obtained in experiments at the VEPP-2000 e+e- collider are presented. The reactions e+e− → ηπ+π−, e+e− → K+K−, e+e− → π+π−π0, e+e− → ωπ0, e+e− → ωη have been studied in the energy region 1.05–2.00 GeV. The neutron and proton electromagnetic form factors have been measured in the energy range from the threshold up to 2 GeV. The result of the search of the rare process e+e− → η′ is also presented.

A search for direct production of C-even resonances a2(1320) and f2(1270) in e+e− annihilation was performed with SND detector at VEPP-2M e+e− collider. The upper limits of electronic widths of these mesons were obtained at 90% confidence level: Γ(a2(1320)→e+e−)<0.56 eV, Γ(f2(1270)→e+e−)<0.11 eV.

The e + e −→ηγ→7γ process was studied in the energy range 2E=600–1060 MeV with an SND detector on a VEPP-2M e + e − collider. The decay branching ratios B(φ→ηγ)=(1.353±0.011±0.052)×10−2, B(ω→ηγ)=(4.62±0.71±0.18)×10−4, and B(ρ→ηγ)=(2.73±0.31±0.15)×10−4 were measured.

Recent results on various cross sections of e+e−→hadrons obtained with the SND and CMD3 detectors at the VEPP-2000 collider in the energy range up to 2 GeV are presented. The final states studied include e+e−→π+π−, K+K−, π+π−π0, π+π−π0π0, ηπ+π−, ωη, ηγ and others. The measured cross sections are important since they contribute to the total hadronic cross section, muon g-2 and parameters of excited vector mesons. The nucleon-antinucleon production at threshold was also studied.

Calibration of the three layer NaI(Tl) spherical calorimeter of the SND detector using electron-positron scattering events is described. Energy resolution of 5%(FWHM/2.36) for 500 MeV photons was achieved.

A new experiment is suggested in order to investigate the positron yield at the exit of crystal tungsten targets of different thicknesses submitted to 10 GeV electron beam at one of the SPS CERN transfer lines. The Set-up consists of the beam control counters, targets mounted on the goniometer, positron detector and photon detector. The positron detector is based mainly on a drift chamber inserted between the poles of the magnet. It allows to reconstruct the track of the charged particles, to define the vertex coordinates and initial angle of the particles at the exit of the target, to measure the total and transverse momenta. A Monte Carlo simulation corresponding to the theoretical description of chanelling radiation and also numerical calculation were provided for the estimations of the expected distributions and detector response. The optimization of the Set-up is considered, as well as the status of the project in general.

The process e + e -→ µ + µ -has been studied with SND detector at VEPP-2M e + e -collider in the vicinity of φ(1020) resonance.The product of branching ratios of φ meson into leptons B(φ → µ + µ -) • B(φ → e + e -) = (3.14 ± 0.22 ± 0.14) • 10 -4 was measured from the interference in the cross section of the process e + e -→ µ + µ -.The branching ratio B(φ → µ + µ -) = (3.30± 0.45 ± 0.32) • 10 -4 was obtained.

The current status of experiments with SND detector at VEPP-2M e^+e^- collider in the energy range 2E_0=400-1400 MeV and recent results of data analysis for $\phi$, $\omega$ and $\rho$ decays and e^+e^- annihilation into hadrons are presented.

Results of the first measurements of the cross sections for the e+e−→pp¯ and e+e−→nn¯ with the SND detector are presented. The analysis is based on data with integrated luminosity of 2.8pb−1, collected in 2011 by the SND detector at the VEPP-2000 e+e− collider in the energy range above nucleon production threshold.

Preliminary results of the SND experiment at the VEPP-2000 e+e− collider are presented. Data corresponding to about 40 pb−1 of integrated luminosity were collected in the e+e− c.m. energy range from 1.05 to 2.00 GeV. The cross sections for e+e− → ωπ0, π+π−4π0, , have been measured.

The results of the measurement of the $e^+e^- \to n \bar{n}$ cross section and effective neutron timelike form factor are presented. The data taking was carried out in 2020-2021 at the VEPP-2000 $e^+e^-$ collider in the center-of-mass energy range from 1891 to 2007 MeV. The general purpose nonmagnetic detector SND is used to detect neutron-antineutron events. The event selection is performed using the time-of-flight technique. The measured cross section is 0.4-0.6 nb. The neutron form factor in the energy range under study varies from 0.3 to 0.2.

The process e+e−→ωπ0→π+π−π0π0 is studied in the center-of-mass energy region 1.05–2.00 GeV using data with an integral luminosity of about 35 pb−1 collected with the SND detector at the VEPP-2000 e+e− collider. In the energy range under study, the value of the measured Born cross section varies from 0.7 to 18 nb. The statistical uncertainty of the cross section is 2%–23%, while the systematic uncertainty is in the range of 3.0%–14.2%. The results are consistent with previous measurements but have better accuracy.4 MoreReceived 6 September 2023Accepted 1 November 2023DOI:https://doi.org/10.1103/PhysRevD.108.092012Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article’s title, journal citation, and DOI. Funded by SCOAP3.Published by the American Physical SocietyPhysics Subject Headings (PhySH)Research AreasHadron productionLepton-lepton interactionsPhysical SystemsLight mesonsPropertiesForm factorsParticles & Fields

We review here recent results on [Formula: see text] annihilation to hadrons below 2 GeV obtained with the SND detector at the VEPP-2000 collider. Among others we report cross sections and dynamics properties for the [Formula: see text], [Formula: see text], [Formula: see text], and [Formula: see text].

Results are presented from measuring the e+e− → n¯n cross section and effective neutron timelike form factor. Data are collected in 2020–2021 at the VEPP-2000 e+e− collider in the 1891 to 2007 MeV center-of-mass range of energies. The general purpose nonmagnetic SND detector is used to detect neutron–antineutron events. The time-of-flight approach is used to select n¯n events. The measuredcross section is 0.4–0.6 nbn. The neutron form factor in the investigated range of energies varies from 0.3 to 0.2.

The φ(1020)→ηγ→3π 0 γ decay is studied in the SND experiment at the VEPP-2M e + e − collider. The measurements give a branching ratio Bφ→ ηγ)=(1.246±0.025±0.057)%.

The review of the SND results of the $e^+e^-\to\pi^+\pi^-\pi^0$ process study in the energy range $\sqrt[]{s}=0.42$ -- 1.38 GeV at VEPP-2M collider, based on about $2\times 10^6$ selected events, is presented. The total cross section, parameters of the $\rho$, $\omega$, $\phi$ resonances, and $\omega^\prime$, $\omega^{\prime\prime}$ states were obtained. It was found that $\rho\pi$ and $\omega\pi^0$ intermediate states describe the reaction dynamics. The experimental data cannot be described by a sum of only $\omega$, $\phi$, $\omega^\prime$ and $\omega^{\prime\prime}$ resonances contributions. This can be interpreted as a manifestation of the $\rho\to 3\pi$ decay, suppressed by $G$-parity, with relative probability $B(\rho\to 3\pi) = (1.01\pm^{0.54}_{0.36}\pm 0.034) \times 10^{-4}$.

The review of results on the ρ, ω, and ϕ radiative and rare hadronic decays, measured in SND and CMD-2 experiments at VEPP-2M e + e − -collider is presented. Comparison with KLOE measurements and theoretical models is given.

The cross section of the process ${e}^{+}{e}^{\ensuremath{-}}\ensuremath{\rightarrow}{\ensuremath{\mu}}^{+}{\ensuremath{\mu}}^{\ensuremath{-}}$ was measured in the spherical neutral detector experiment at the VEPP-2M ${e}^{+}{e}^{\ensuremath{-}}$ collider in the energy region $\sqrt{s}=980$, 1040--1380 MeV. The event numbers of the process ${e}^{+}{e}^{\ensuremath{-}}\ensuremath{\rightarrow}{\ensuremath{\mu}}^{+}{\ensuremath{\mu}}^{\ensuremath{-}}$ were normalized to the integrated luminosity measured using ${e}^{+}{e}^{\ensuremath{-}}\ensuremath{\rightarrow}{e}^{+}{e}^{\ensuremath{-}}$ and ${e}^{+}{e}^{\ensuremath{-}}\ensuremath{\rightarrow}\ensuremath{\gamma}\ensuremath{\gamma}$ processes. The ratio of the measured cross section to the theoretically predicted value is $1.006\ifmmode\pm\else\textpm\fi{}0.007\ifmmode\pm\else\textpm\fi{}0.016$ and $1.005\ifmmode\pm\else\textpm\fi{}0.007\ifmmode\pm\else\textpm\fi{}0.018$ in the first and second case, respectively. Using results of the measurements, the electromagnetic running coupling constant $\ensuremath{\alpha}$ in the energy region $\sqrt{s}=1040--1380\text{ }\text{ }\mathrm{MeV}$ was obtained $⟨1/\ensuremath{\alpha}⟩=134.1\ifmmode\pm\else\textpm\fi{}0.5\ifmmode\pm\else\textpm\fi{}1.2$ and this is in agreement with theoretical expectation.

Abstract The process $$e^+e^-\rightarrow K^+K^-\pi ^0$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mrow> <mml:msup> <mml:mi>e</mml:mi> <mml:mo>+</mml:mo> </mml:msup> <mml:msup> <mml:mi>e</mml:mi> <mml:mo>-</mml:mo> </mml:msup> <mml:mo>→</mml:mo> <mml:msup> <mml:mi>K</mml:mi> <mml:mo>+</mml:mo> </mml:msup> <mml:msup> <mml:mi>K</mml:mi> <mml:mo>-</mml:mo> </mml:msup> <mml:msup> <mml:mi>π</mml:mi> <mml:mn>0</mml:mn> </mml:msup> </mml:mrow> </mml:math> is studied with the SND detector at the VEPP-2000 $$e^+e^-$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mrow> <mml:msup> <mml:mi>e</mml:mi> <mml:mo>+</mml:mo> </mml:msup> <mml:msup> <mml:mi>e</mml:mi> <mml:mo>-</mml:mo> </mml:msup> </mml:mrow> </mml:math> collider. Basing on data with an integrated luminosity of 26.4 $$\hbox {pb}^{-1}$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msup> <mml:mtext>pb</mml:mtext> <mml:mrow> <mml:mo>-</mml:mo> <mml:mn>1</mml:mn> </mml:mrow> </mml:msup> </mml:math> we measure the $$e^+e^-\rightarrow K^+K^-\pi ^0$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mrow> <mml:msup> <mml:mi>e</mml:mi> <mml:mo>+</mml:mo> </mml:msup> <mml:msup> <mml:mi>e</mml:mi> <mml:mo>-</mml:mo> </mml:msup> <mml:mo>→</mml:mo> <mml:msup> <mml:mi>K</mml:mi> <mml:mo>+</mml:mo> </mml:msup> <mml:msup> <mml:mi>K</mml:mi> <mml:mo>-</mml:mo> </mml:msup> <mml:msup> <mml:mi>π</mml:mi> <mml:mn>0</mml:mn> </mml:msup> </mml:mrow> </mml:math> cross section in the center-of-mass energy range from 1.28 up to 2 GeV. The measured mass spectrum of the $$K\pi $$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mrow> <mml:mi>K</mml:mi> <mml:mi>π</mml:mi> </mml:mrow> </mml:math> system indicates that the dominant mechanism of this reaction is the transition through the $$K^{*}(892)K$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mrow> <mml:msup> <mml:mi>K</mml:mi> <mml:mrow> <mml:mrow /> <mml:mo>∗</mml:mo> </mml:mrow> </mml:msup> <mml:mrow> <mml:mo>(</mml:mo> <mml:mn>892</mml:mn> <mml:mo>)</mml:mo> </mml:mrow> <mml:mi>K</mml:mi> </mml:mrow> </mml:math> intermediate state. The cross section for the $$\phi \pi ^0$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mrow> <mml:mi>ϕ</mml:mi> <mml:msup> <mml:mi>π</mml:mi> <mml:mn>0</mml:mn> </mml:msup> </mml:mrow> </mml:math> 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 $$\phi \pi ^0$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mrow> <mml:mi>ϕ</mml:mi> <mml:msup> <mml:mi>π</mml:mi> <mml:mn>0</mml:mn> </mml:msup> </mml:mrow> </mml:math> and $$K^*K$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mrow> <mml:msup> <mml:mi>K</mml:mi> <mml:mo>∗</mml:mo> </mml:msup> <mml:mi>K</mml:mi> </mml:mrow> </mml:math> amplitudes. It is found that the interference gives sizable contribution to the measured $$e^+e^- \rightarrow \phi \pi ^0\rightarrow K^+K^-\pi ^0$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mrow> <mml:msup> <mml:mi>e</mml:mi> <mml:mo>+</mml:mo> </mml:msup> <mml:msup> <mml:mi>e</mml:mi> <mml:mo>-</mml:mo> </mml:msup> <mml:mo>→</mml:mo> <mml:mi>ϕ</mml:mi> <mml:msup> <mml:mi>π</mml:mi> <mml:mn>0</mml:mn> </mml:msup> <mml:mo>→</mml:mo> <mml:msup> <mml:mi>K</mml:mi> <mml:mo>+</mml:mo> </mml:msup> <mml:msup> <mml:mi>K</mml:mi> <mml:mo>-</mml:mo> </mml:msup> <mml:msup> <mml:mi>π</mml:mi> <mml:mn>0</mml:mn> </mml:msup> </mml:mrow> </mml:math> cross section below 1.7 GeV.

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 &lt; $$ \sqrt{s} $$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msqrt> <mml:mi>s</mml:mi> </mml:msqrt> </mml:math> &lt; 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 $$ \sqrt{s} $$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msqrt> <mml:mi>s</mml:mi> </mml:msqrt> </mml:math> &gt; 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.

Upper bound Br(η→π0π0)<6·10−4 with 90% confidence is reported from the SND experiment at the VEPP-2M collider.

Abstract The project of the new spherical neutral detector tracking system for experiments at VEPP-2000 e + e − collider is presented. The tracking system consists of a drift and a proportional chambers in a common gas volume. The drift chamber provides 9 measurements along the track for charged particles within 94% solid angle. Design angular resolutions for radial tracks are σ φ =0.18°, σ θ =0.3° , the vertex resolution is σ R =0.2 mm . The design of the tracking system, electric field configuration, electronics, and detector simulation are described.