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D. B. Shwartz

Publications and source records attributed to D. B. Shwartz.

At least 19 recordsLinked to original sources
arXiv2026

Neutral kaon mass measurement with the CMD-3 derector at VEPP-2000

Using more than 600 thousand $K_{S}^{0}\toπ^{+}π^{-}$ decays from the $e^{+}e^{-}\toϕ(1020)\to K_{S}^{0}K_{L}^{0}$ reaction, the neutral kaon mass has been measured with the CMD-3 detector at the VEPP-2000 collider. Using the beam energies control by the back-scattering laser light photons, and a calibration to the world average $ϕ$-meson mass, the neutral kaon mass is determind to be m($K^0$) = 497.587 $\pm$ 0.004(stat.) $\pm$ 0.008(syst.) $\pm$ 0.009(calibr.) \mevcc, where the first uncertainty is statistical, the second is systematic, and the third is the uncertainty from the energy calibration.

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arXiv2026

Evidence of the $e^+ e^-\to f_1(1285)$ reaction with the CMD-3 detector at VEPP-2000

A search for the $e^+ e^-\to f_1(1285)$ reaction is performed with the CMD-3 detector at the VEPP-2000 collider. Data from a scan in the center-of-mass energy range Ec.m.=1.20--1.36 GeV with 109.1 pb$^{-1}$ of the integrated luminosity is used. A dedicated 51.7 pb$^{-1}$ have been collected at the $f_1(1285)$ resonance peak energy Ec.m.=1282 MeV, where $26.5 \pm 7.4$ events have been found in the $e^+ e^-\toηπ^0π^0$ reaction. No indication of the signal is observed in the scan data. We interpret the result as 4.5$σ$ evidence of the C-even resonance production in the $e^+ e^-\to f_1(1285)\toηπ^0π^0$ reaction via the two-photon interaction. The production cross section is found to be $σ(e^+ e^-\to f_1) = 0.074 \pm 0.021 \pm 0.010$ nb, and the corresponding branching fraction to the $e^+ e^-$ pair is $B(f_1(1285)\to e^+e^-) = (8.3 \pm 2.3 \pm 1.1)\times 10^{-9}$.

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arXiv2026

Study of the proccess $e^+e^-\to \pi^+\pi^-\pi^0\pi^0\eta$ in the c.m. energy range 1.6--2.0 GeV with the CMD-3 detector

The cross section of the process $e^+e^- \to \pi^+\pi^-\pi^0\pi^0\eta$ has been measured using a data sample with the integrated luminosity of 372 pb$^{-1}$ collected with the CMD-3 detector at the VEPP-2000 $e^+e^-$ collider. 6300$\pm$145 signal events have been selected in the center-of-mass energy range 1.6--2.0 GeV. The total systematic uncertainty of the cross section is about 10\%. The production dynamics is dominated by the $\omega(782)\pi^0\eta$ final state with a possible small contribution of the $a_0(980)$ resonance in the $\pi^0\eta$ combination. We also observe a presence of the $\rho(770)^{\pm}$ resonance signal in the $\pi^{\pm}\pi^0$ invariant mass distribution.

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arXiv2024

Measurement of the $e^+e^-\toπ^+π^-$ cross section from threshold to 1.2 GeV with the CMD-3 detector

The cross section of the process $e^+e^-\toπ^+π^-$ has been measured in the center of mass energy range from 0.32 to 1.2 GeV with the CMD-3 detector at the electron-positron collider VEPP-2000. The measurement is based on a full dataset collected below 1 GeV during three data taking seasons, corresponding to an integrated luminosity of about 62 pb$^{-1}$. In the dominant $ρ$-resonance region, a systematic uncertainty of 0.7% has been reached. At energies around $ϕ$-resonance the $π^+π^-$ production cross section was measured for the first time with high beam energy resolution. The forward-backward charge asymmetry in the $π^+π^-$ production has also been measured. It shows a strong deviation from the theoretical prediction based on the conventional scalar quantum electrodynamics framework, and it is in good agreement with the generalized vector-meson-dominance and dispersive-based predictions. The impact of the presented results on the evaluation of the hadronic contribution to the anomalous magnetic moment of muon is discussed.

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arXiv2024

Measurement of the pion form factor with CMD-3 detector and its implication to the hadronic contribution to muon (g-2)

The cross section of the process $e^+e^-\toπ^+π^-$ has been measured in the center-of-mass energy range from 0.32 to 1.2 GeV with the CMD-3 detector at the electron-positron collider VEPP-2000. The measurement is based on an integrated luminosity of about 88 pb$^{-1}$, of which 62 pb$^{-1}$ represent a complete dataset collected by CMD-3 at center-of-mass energies below 1 GeV. In the dominant region near the $ρ$ resonance a systematic uncertainty of 0.7% was achieved. The implications of the presented results for the evaluation of the hadronic contribution to the anomalous magnetic moment of the muon are discussed.

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arXiv2022

Experimental study of the $e^+e^-\to n\bar n$ process at the VEPP-2000 $e^+e^-$ collider with the SND detector

The process $e^+e^-\to n\bar n$ 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 nnbar 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.

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arXiv2021

Study of the process $e^+e^- \to ηηγ$ in the energy range $\sqrt{s} = \mbox{1.17--2.00}$ GeV with the SND detector

The process $e^+e^-\toηηγ$ 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 $e^+e^-\toηηγ$ 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 $e^+e^-\toηηγ$ cross section is consistent with the $e^+e^-\toϕη$ measurement in the $ϕ\to K^+ K^-$ mode. The search for radiative processes contributing to the $e^+e^-\toηηγ$ cross section is performed, and no significant signal is observed.

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arXiv2020

Measurement of the $e^+e^- \to K^+ K^- π^0$ cross section with the SND detector

The process $e^+e^-\to K^+K^-π^0$ is studied with the SND detector at the VEPP-2000 $e^+e^-$ collider. Basing on data with an integrated luminosity of 26.4~pb$^{-1}$ we measure the $e^+e^-\to K^+K^-π^0$ cross section in the center-of-mass energy range from 1.28 up to 2 GeV. The measured mass spectrum of the $Kπ$ system indicates that the dominant mechanism of this reaction is the transition through the $K^{\ast}(892)K$ intermediate state. The cross section for the $ϕπ^0$ 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 $ϕπ^0$ and $K^\ast K$ amplitudes. It is found that the interference gives sizable contribution to the measured $e^+e^- \to ϕπ^0\to K^+K^-π^0$ cross section below 1.7 GeV.

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arXiv2020

Measurement of the $e^+e^- \toπ^+π^- $ process cross section with the SND detector at the VEPP-2000 collider in the energy region $0.525<\sqrt{s}<0.883$ GeV

The cross section of the process $e^+ e^-\toπ^+π^-$ has been measured in the Spherical Neutral Detector (SND) experiment at the VEPP-2000 $e^+e^-$ collider VEPP-2000 in the energy region $525 <\sqrt[]{s} <883$ 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 $\sqrt{s}>0.600$ GeV. The $ρ$ meson parameters are obtained as $m_ρ= 775.3\pm 0.5\pm 0.6$ MeV, $Γ_ρ= 145.6\pm 0.6\pm 0.8$ MeV, $B_{ρ\to e^+ e^-}\times B_{ρ\toπ^+π^-} = (4.89\pm 0.02\pm 0.04)\times 10^{-5}$, and the parameters of the $e^+ e^-\toω\toπ^+π^-$ process, suppressed by $G$-parity, as $B_{ω\to e^+ e^-}\times B_{ω\toπ^+π^-}= (1.32\pm 0.06\pm 0.02)\times 10^{-6} $ and $ϕ_{ρω} = 110.7\pm 1.5\pm1.0$ degrees.

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arXiv2020

Study of dynamics of the process $e^+e^-\to π^+π^-π^0$ in the energy range 1.15--2.00 GeV

The dynamics of the process $ e^+e^- \to 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 $e^+e^-$ collider. The Dalitz plot distribution and $π^+π^-$ mass spectrum are analyzed in a model including the intermediate states $ρ(770)π$, $ρ(1450)π$, and $ωπ^0$. As a result, the energy dependences of the $ρ(770)π$ and $ρ(1450)π$ cross sections and the relative phases between the $ρ(770)π$ amplitude and the $ρ(1450)π$ and $ωπ^0$ amplitudes are obtained. The $ρ(1450)π$ cross section has a peak in the energy region of the $ω(1650)$ resonance (1.55-1.75 GeV). In this energy range the contributions of the $ρ(770)π$ and $ρ(1450)π$ states are of the same order of magnitude. No resonance structure near 1.65 GeV is observed in the $ρ(770)π$ cross section. We conclude that the intermediate state $ρ(1450)π$ gives a significant contribution to the decay of $ω(1650)\toπ^+π^-π^0$, whereas the $ρ(770)π$ mechanism dominates in the decay $ω(1420)\toπ^+π^-π^0$.

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arXiv2020

Study of the process $e^+e^- \to ηπ^0γ$ in the energy range $\sqrt{s} = \mbox{1.05-2.00}$ GeV with the SND detector

The process $e^+e^-\toηπ^0γ$ 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 $e^+e^-\toηπ^0γ$ 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 $e^+e^-\toωη\toηπ^0γ$ is consistent with previous measurements in the $e^+e^-\toπ^+π^-π^0η$ mode. It is found, with a significance of 5.6$σ$, that the process $e^+e^-\toηπ^0γ$ 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. $e^+e^-\to a_{0}(1450)γ$, is measured. It is found to be 15-20 pb in the wide energy range from 1.3 to 1.9 GeV.

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arXiv2020

Measurement of the $e^{+}e^{-}\rightarrowηπ^{+}π^{-}$ cross section with the CMD-3 detector at the VEPP-2000 collider

The cross section of the process $e^{+}e^{-}\rightarrowηπ^{+}π^{-}$ is measured using the data collected with the CMD-$3$ detector at the VEPP-$2000$ collider in the center-of-mass energy range from $1.1$ to $2.0$ GeV. The decay mode $η\rightarrowγγ$ is used for $η$ meson reconstruction in the data sample corresponding to an integrated luminosity of $78.3$ pb$^{-1}$. The energy dependence of the $e^{+}e^{-}\rightarrowηπ^{+}π^{-}$ cross section is fitted within the framework of vector meson dominance in order to extract the $Γ(ρ(1450)\rightarrow{^{+}e^{-}})\mathcal{B}(ρ(1450)\rightarrowηπ^{+}π^{-})$ and the $Γ(ρ(1700)\rightarrow{e^{+}e^{-}})\mathcal{B}(ρ(1700)\rightarrowηπ^{+}π^{-})$ products. Based on conservation of vector current, the analysed data are used to test the relationship between the $e^{+}e^{-}\rightarrowηπ^{+}π^{-}$ cross section and the spectral function in $τ^-\rightarrowηπ^-π^0ν_τ$ decay. The $e^{+}e^{-}\rightarrowηπ^{+}π^{-}$ cross section measured with the CMD-$3$ detector is in good agreement with the previous measurements.

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arXiv2019

Search for direct production of the $f_1(1285)$ resonance in $e^+e^-$ collisions

A search for direct production of the $f_1(1285)$ 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 $e^+e^-\to f_1(1285)$ candidate events are found at the peak of the resonance and zero events beyond the resonance. The significance of the $e^+e^-\to f_1(1285)$ signal is $2.5σ$. The cross section at the maximum of the resonance is found to be $σ(e^+e^-\to f_1)=45^{+33}_{-24}$ pb. The corresponding branching fraction $B(f_1(1285)\to e^+e^-)=(5.1^{+3.7}_{-2.7})\times 10^{-9}$. We consider this result as a first indication of the process $e^+e^-\to f_1(1285)$. The measured branching fraction is consistent with the theoretical prediction.

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arXiv2019

Study of the process $e^+e^-{\to}K^+K^-η$ with the CMD-3 detector at the VEPP-2000 collider

The process $e^+e^-{\to}K^+K^-η$ has been studied in the center-of-mass energy range from 1.59 to 2.007\,GeV using the data sample of 59.5 pb$^{-1}$, collected with the CMD-3 detector at the VEPP-2000 $e^+e^-$ collider in 2011, 2012 and 2017. The $K^+K^-η$ final state is found to be dominated by the contribution of the $ϕ(1020)η$ intermediate state. The cross section of the process $e^+e^-{\to}ϕ(1020)η$ has been measured with a systematic uncertainty of 5.1$\%$ on the base of 3009 $\pm$ 67 selected events. The obtained cross section has been used to calculate the contribution to the anomalous magnetic moment of the muon: $a_μ^{ϕη}(E<1.8\, {\rm GeV})=(0.321 \pm 0.015_{\rm stat} \pm 0.016_{\rm syst}) \times 10^{-10}$, $a_μ^{ϕη}(E<2.0\, {\rm GeV})=(0.440 \pm 0.015_{\rm stat} \pm 0.022_{\rm syst}) \times 10^{-10}$. From the cross section approximation the $ϕ(1680)$ meson parameters have been determined with better statistical precision, than in previous studies.

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arXiv2018

Measurement of the $e^+e^- \to π^0γ$ cross section in the energy range 1.075--2 GeV at SND

The process $e^+e^- \to π^0γ$ is studied with the SND detector at the VEPP-2000 $e^+e^-$ collider. Basing on data with an integrated luminosity of 41 pb$^{-1}$ recorded in 2010-2012 we measure the $e^+e^- \to π^0γ$ 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 $e^+e^- \to π^0γ$ is studied for the first time.

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arXiv2018

Search for the process $\mathbf{e^+e^- \toη}$

A search for the rare decay $η\rightarrow e^+e^-$ is performed using the inverse process $e^+e^- \rightarrow η$ in the decay mode $η\toπ^0π^0π^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_ηc ^2\approx 548 $ MeV, and set the upper limit $ {\cal B} (η\rightarrow e^+ e^-) < 7 \times 10^{-7} $ at the 90\% confidence level.

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arXiv2017

Study of the process $e^+e^- \to K^+K^-$ in the center-of-mass energy range 1010--1060~MeV with the CMD-3 detector

The process $e^+e^- \to K^+K^-$ has been studied using $1.7 \times 10^6$ events from a data sample corresponding to an integrated luminosity of 5.7 pb$^{-1}$ collected with the CMD-3 detector in the center-of-mass energy range 1010--1060 MeV. The cross section measured with an about 2\% systematic uncertainty and it is used to calculate the contribution to the anomalous magnetic moment of the muon $a_μ^{K^+K^-} = (19.33 \pm 0.40) \times 10^{-10}$, and to obtain the $ϕ(1020)$ meson parameters. We consider the relationship between the $e^+e^- \to K^+K^-$ and $e^+e^- \to K^0_SK^0_L$ cross sections and compare it to the theoretical expectations.

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