The process \(e^+e^-\to\eta\pi^0\gamma\) 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 \(e^+e^-\to\eta\pi^0\gamma\) cross section is measured for the first time. It is shown that the dominant mechanism of this reaction is the transition through the \(\omega\eta\) intermediate state. The measured cross section of the subprocess \(e^+e^-\to\omega\eta\to\eta\pi^0\gamma\) is consistent with previous measurements in the \(e^+e^-\to\pi^+\pi^-\pi^0\eta\) mode. It is found, with a significance of 5.6\(\sigma\), that the process \(e^+e^-\to\eta\pi^0\gamma\) 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. \(e^+e^-\to a_{0}(1450)\gamma\), is measured. It is found to be 15-20 pb in the wide energy range from 1.3 to 1.9 GeV.
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.
Phys. Rev. D 91, 092010 (2015) 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 cross section of the process \(e^{+}e^{-}\rightarrow\eta\pi^{+}\pi^{-}\) 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 \(\eta\rightarrow\gamma\gamma\) is used for \(\eta\) meson reconstruction in the data sample corresponding to an integrated luminosity of \(78.3\) pb\(^{-1}\). The energy dependence of the \(e^{+}e^{-}\rightarrow\eta\pi^{+}\pi^{-}\) cross section is fitted within the framework of vector meson dominance in order to extract the \(\Gamma(\rho(1450)\rightarrow{^{+}e^{-}})\mathcal{B}(\rho(1450)\rightarrow\eta\pi^{+}\pi^{-})\) and the \(\Gamma(\rho(1700)\rightarrow{e^{+}e^{-}})\mathcal{B}(\rho(1700)\rightarrow\eta\pi^{+}\pi^{-})\) products. Based on conservation of vector current, the analysed data are used to test the relationship between the \(e^{+}e^{-}\rightarrow\eta\pi^{+}\pi^{-}\) cross section and the spectral function in \(\tau^-\rightarrow\eta\pi^-\pi^0\nu_\tau\) decay. The \(e^{+}e^{-}\rightarrow\eta\pi^{+}\pi^{-}\) cross section measured with the CMD-\(3\) detector is in good agreement with the previous measurements.
Phys. Rev. D 91, 052013 (2015) In the experiment with the SND detector at the VEPP-2000 $e^+e^-$ collider
the cross section for the process $e^+e^-\to\eta\pi^+\pi^-$ 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 $e^+e^-\to\eta\pi^+\pi^-$ cross section has been fitted with
the vector-meson dominance model. From this fit the product of the branching
fractions $B(\rho(1450)\to\eta\pi^+\pi^-)B(\rho(1450)\to e^+e^-)$ has been
extracted and compared with the same products for $\rho(1450)\to\omega\pi^0$
and $\rho(1450)\to\pi^+\pi^-$ decays. The obtained cross section data have been
also used to test the conservation of vector current hypothesis.
Phys. Rev. D 90, 112007 (2014) The process $e^+e^-\to n\bar{n}$ 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 $e^+e^-\to n\bar{n}$ cross section and
effective neutron form factor have been measured.
The process \(e^+e^- \to \pi^0\gamma\) 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 \(e^+e^- \to \pi^0\gamma\) 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 \(e^+e^- \to \pi^0\gamma\) is studied for the first time.
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.
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.
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