arXiv subjects

A. S. Kasaev

Publications and source records attributed to A. S. Kasaev.

At least 19 recordsLinked to original sources

arXiv2026

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

The cross section of the process $e^+e^- \to π^+π^-π^0π^0η$ 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 $ω(782)π^0η$ final state with a possible small contribution of the $a_0(980)$ resonance in the $π^0η$ combination. We also observe a presence of the $ρ(770)^{\pm}$ resonance signal in the $π^{\pm}π^0$ invariant mass distribution.

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arXiv2026

Search for the process $e^+e^-\to f_1(1285)$ at the SND detector

In the experiment with the SND detector at the VEPP-2000 $e^+e^-$ collider, a search is performed for the direct production of the $C$-even $f_1(1285)$ resonance in $e^+e^-$ collisions. The analysis is based on data with an integrated luminosity of about 200 pb$^{-1}$, accumulated in the center-of-mass energy range of 1.14--1.46 GeV, of which about 72 pb$^{-1}$ were recorded near the maximum of the $f_1(1285)$ resonance. The $f_1(1285)$ production cross section at the resonance maximum $σ(e^+e^-\to f_1)=(31\pm 13\pm 2)$ pb and the branching fraction $B(f_1(1285)\to e^+e^-)=(3.5\pm 1.4\pm 0.3)\times 10^{-9}$ have been measured. The significance of the observation of the $e^+e^-\to f_1(1285)$ process is $2.5σ$. Since the significance is low, we also present the upper limits at the 90% confidence level: $σ(e^+e^-\to f_1)<48\mbox{ pb}$ and $B(f_1(1285)\to e^+e^-)<5.4\times 10^{-9}$.

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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

Measurement of the neutron timelike electric and magnetic form factors ratio at the VEPP-2000 $e^+e^-$ collider

In the experiment to study the e+e->n+anti n process at the VEPP-2000 $e^+e^-$ collider, the ratio |GE|/|GM| of the neutron timelike electric and magnetic form factors has been measured. The experiment was carried out with the SND detector in the center-of-mass energy range 1890-2000 MeV in eight energy points with an integrated luminosity of 83 inv.pb. The |GE|/|GM| ratio is determined by the analyzing the distribution of the polar angle of the produced antineutron. The measured |GE|/|GM| value in the energy range under study is between 1.0 and 1.5 with an average value of 1.21+-0.13.

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arXiv2025

Measurement of the $e^+e^-\toηγ$ cross section near the $ϕ(1020)$ resonance with the SND detector

In the experiment with the SND detector at the VEPP-2000 $e^+e^-$ collider, the $e^+e^-\toηγ$ cross section is measured in the energy range $E = 980 - 1060$ MeV. The measurement is carried out in the $η\to 2γ$ decay mode. Data with an integrated luminosity of 73 pb$^{-1}$ collected in 2018 and 2024 are used in the analysis. The measured cross section is the most accurate to date and is higher compared to other measurements. From the fit to the cross section data with the vector meson dominance model, the value of the product of the branching fractions $B(ϕ\to e^+e^-)B(ϕ\to ηγ)$ has been obtained.

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arXiv2024

Measurement of the $e^+e^-\to K_SK_L$ cross section near the $ϕ(1020)$ resonance with the SND detector

The cross section for the $e^+e^-\to K_SK_L$ process is measured in the center-of-mass energy range from 1000 MeV to 1100 MeV in the experiment with the SND detector at the VEPP-2000 $e^+e^-$ collider. The measurement is carried out in the $K_S\to 2π^0$ decay mode. Data with an integrated luminosity of 20 pb$^{-1}$ recorded in 2018 at 18 energy points are used in the analysis. The systematic uncertainty in the measured cross section at the maximum of the $ϕ$ resonance is 0.9%. The mass, width of the $ϕ$ meson, and the product of the branching fractions $B(ϕ\to K_SK_L)B(ϕ\to e^+e^-)$ are determined from the fit to the cross-section energy dependence.

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arXiv2024

Cross section of the process $e^+e^-\to n\bar{n}$ near the threshold

The $e^+e^-\to n\bar{n}$ cross section was measured at center of mass (c.m.) energies from the threshold to 1908 MeV. The experiment to measure the cross section has been carried out at the VEPP-2000 $e^+e^-$ collider in 13 energy points. The SND detector is used to detect the produced neutron-antineutrons ($n\bar{n}$) events. A special time measurement system on the calorimeter was used to select the time-delayed $n\bar{n}$ events. The measured $e^+e^-\to n\bar{n}$ cross section is 0.4--0.6 nb. The neutron effective timelike form factor in the energy range under study varies from 0.3 to 0.6.

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arXiv2024

Search for the process $\mathbf{\it e^+e^-\toη^{\prime}γ}$ in the energy range $\mathbf{\it \sqrt{s}}$ = 1.075 -- 2 GeV

The results of the search for the $e^+e^-\toη^{\prime}γ$ process in the center-of-mass energy range from 1.075 to 2 GeV are presented. We analyze data with an integral luminosity of 746 pb$^{-1}$ accumulated with the SND detector at the $e^+e^-$ collider VEPP-2000 in 2010--2024. The $η^{\prime}\toηπ^0π^0$ decay is used in the analysis, with the subsequent $η$ and $π^0$ decays into $γγ$. Upper limits not exceeding 13 pb have been set on the $e^+e^-\toη^{\prime}γ$ cross section at the 90\% confidence level.

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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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arXiv2023

Measurement of the neutron timelike electromagnetic form factor with the SND detector

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.

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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

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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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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