The e + e − → π 0 π 0 γ 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 → π 0 π 0 γ ) = (6 . 6 +1 . 4 − 0 . 8 ± 0 . 6) · 10 − 5 and B ( ρ → π 0 π 0 γ ) = (4 . 1 +1 . 0 − 0 . 9 ± 0 . 3) · 10 − 5 were obtained.

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.

Current status and last results of the Spherical Neutral Detector (SND) calorimeter upgrade are described. The main part of SND detector is a three-layer spherical NaI(Tl) electromagnetic calorimeter (EMC). The total thickness of NaI(Tl) in the calorimeter is 35 cm. The vacuum phototriodes (VPT) are used as photosensitive devices for the calorimeter counters. The quantum efficiency of VPT is about 15%, the average gain is 10, and the light collection efficiency is about 10%. New spectrometric channel of EMC was designed and implemented. It consists of a NaI(Tl) crystal, a vacuum phototriode, a charge-sensitive preamplifier a shaper and digitizing modules. The digitization is performed by 6 ADCs AD9228BCPZ-40 (4 channel, 12 bits, 40 MBPS) and the data go in serial form to the SoC Xilinx Zynq-7000. This SoC is basically a combination of FPGA programmable logic and ARM processor. The special algorithm for signal waveform processing was developed to determine time of flight and amplitude with high time (1 ns) and amplitude (250 keV) resolution. The algorithm is based on the invariability of the signal waveform. The waveform calibration procedures are developed and implemented. Successful data taking run was performed with upgraded EMC in 2019.

The cross section for the e + e – → π+π–π0 process in the energy range 1.05–2.00 GeV has been measured using the data collected in the experiment with the Spherical Neutral Detector (SND) at the VEPP-2000 e + e – collider. The obtained results on the cross section are in good agreement with previous measurements by the SND at the VEPP-2M collider and BABAR, but have a better accuracy.

Precise study of the hadrons production in \bm{e^+e^-}𝐞+𝐞− annihilation at low energies provides important information about interactions of light quarks and spectroscopy of their bound states. These studies are especially important for theoretical calculations of the muon \bm{(g-2)}(𝐠−2) via the Standard Model because of the present difference between theoretical and experimental values exceeds three standard deviations. In this report we will discuss current status and recent results obtained by the CMD-3 experiment and will give a brief look to status of the BaBar and Belle II experiments.

At the end of 2016 the SND detector resumed data taking at the upgraded VEPP-2000 e+e− collider. The analysis of data accumulated in 2010-2013 with an integrated lumonosity of 70 pb−1 is continuing. Recent results on measurements of various hadronic cross sections are presented.

Precise study of the hadrons production in\bm{e^+e^-}𝐞+𝐞−annihilation at low energies provides important information aboutinteractions of light quarks and spectroscopy of their bound states.These studies are especially important for theoretical calculations ofthe muon \bm{(g-2)}(𝐠−2)via the Standard Model because of the present difference betweentheoretical and experimental values exceeds three standard deviations.In this report we will discuss current status and recent resultsobtained by the CMD-3 experiment and will give a brief look to status ofthe BaBar and Belle II experiments.

We present recent experimental results for e+e− annihilation into hadrons below 2 GeV obtained with the SND detector at the VEPP-2000 collider. The analyses are based on data collected in the detector runs from 2010 to 2017. During the period from 2014 to 2016 collider and detector underwent significant upgrades which allowed an increase in luminosity and detector efficiency. In particular, results of studying $e^+ e^- \to \pi^+\pi^-$, $\eta \to e^+ e^- $, $e^+ e^- \to n\bar{n} $, $e^+ e^- \to K^+K^-\eta$, $e^+ e^- \to \pi^+\pi^-\eta$, $e^+ e^- \to K_{S}K_{L} \pi^0$, $e^+ e^- \to \pi^+\pi^-\pi^0\eta$, $e^+ e^- \to \omega\pi^0$, $e^+ e^- \to \pi^0\gamma$, and $e^+ e^- \to \pi^+\pi^-4\pi^0$ reactions are considered in this paper.

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.

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.

M. N. Achasov, 2 V. M. Aulchenko, 2 A. Yu. Barnyakov, 2 K. I. Beloborodov, 2 A. V. Berdyugin, 2 D. E. Berkaev, 2 A. G. Bogdanchikov, A. A. Botov, T. V. Dimova, 2 V. P. Druzhinin, 2 V. B. Golubev, 2 L. V. Kardapoltsev, 2 A. S. Kasaev, A. G. Kharlamov, 2 A. N. Kirpotin, I. A. Koop, 2, 3 L. A. Korneev, ∗ A. A. Korol, 2 D. P. Kovrizhin, S. V. Koshuba, A. S. Kupich, 2 N. A. Melnikova, 2 K. A. Martin, A. E. Obrazovsky, A. V. Otboev, E. V. Pakhtusova, K. V. Pugachev, 2 Yu. A. Rogovsky, 2 A. I. Senchenko, 2 S. I. Serednyakov, 2 Z. K. Silagadze, 2 Yu. M. Shatunov, 2 D. A. Shtol, D. B. Shwartz, 2 I. K. Surin, Yu. V. Usov, and A. V. Vasiljev 2 Budker Institute of Nuclear Physics, SB RAS, Novosibirsk, 630090, Russia Novosibirsk State University, Novosibirsk, 630090, Russia Novosibirsk State Technical University, Novosibirsk, 630092, Russia

A search for the rare decay eta -> e(+) e(-) is performed using the inverse process e(+) e(-) -> eta in the decay mode eta -> 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) approximate to 548 MeV, and set the upper limit B(eta -> e(+) e(-)) <7 x 10(-7) at the 90% confidence level.

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

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.

The new spectrometric channel for the Spherical Neutral Detector (SND) electromagnetic calorimeter (EMC) is described. It provides measurement of the calorimeter signal arrival time and amplitude with 1 ns and 250 keV resolutions, respectively. The new electronics is useful for reliable detection of low-speed anti-neutrons from the e(+)e(-) -> n (n) over bar reaction near threshold and needed for increasing the EMC operation rate. The algorithm of determination of signal parameters (time, amplitude) is based on invariability of the signal waveform. We present the procedure of the waveform calibration using signals from cosmic-muon and Bhabha scattering events.

The e(+) e(-) -> KSKL pi(0) cross section is measured in the center-of-mass energy range root 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.

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.

The cross section for the process e + e − → ηK + K − wasmeasured at c.m. energies in the range between 1.56 and 2.00 GeV in an experiment with the SND detector at the VEPP-2000 e + e − collider. The invariant-mass distribution of kaon pairs is consistent with the hypothesis that the transition through the ηφ intermediate state makes a dominant contribution to the transition in question.