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 cross section of the process e+e-\to\mu+\mu- was measured in the SND experiment at the VEPP-2M e+e- collider in the energy region \sqrt{s}=980, 1040 -- 1380 MeV. The event numbers of the process ...e+e-\to\mu+\mu- were normalized to the integrated luminosity measured using e+e-\to e+e- and e+e-\to\gamma\gamma processes. The ratio of the measured cross section to the theoretically predicted value is 1.006\pm 0.007 \pm 0.016 and 1.005 \pm 0.007 \pm 0.018 in the first and second case respectively. Using results of the measurements, the electromagnetic running coupling constant \alpha in the energy region \sqrt{s}=1040 -- 1380 MeV was obtained <1/\alpha> = 134.1\pm 0.5 \pm 1.2 and this is in agreement with theoretical expectation.
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.
The number of \(\psp\) events accumulated by the BESIII experiment from March 3 through April 14, 2009, is determined by counting inclusive hadronic events. The result is \(106.41\times(1.00\pm ...0.81%)\times 10^{6} \). The error is systematic only; the statistical error is negligible.
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.
PismaZh.Eksp.Teor.Fiz.69:8-11,1999 It is discussed the problem of the $\rho^\pm-\rho^0$ mass splitting. It is
suggested to use the $\phi\to\rho\pi\to 3\pi$ decay to measure the
$\rho^{\pm}-\rho^0$ ...mass splitting.
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