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.Comment: 13 pages, 8 figure

Study of the process e+e−→ωπ0→π+π−π0π0e^+e^- \to \omega\pi^0 \to \pi^+\pi^-\pi^0\pi^0 in the energy range 1.05−2.001.05-2.00 GeV with SND

The process $e^+e^- \to \omega\pi^0 \to \pi^+\pi^-\pi^0\pi^0$ is studied in the center-of-mass energy region $1.05-2.00$ GeV using data with an integral luminosity of about 35 pb$^{-1}$ collected with the SND detector at the VEPP-2000 $e^+e^-$ collider. In the energy range under study, the value of the measured Born cross section varies from 0.7 to 18 nb. The statistical uncertainty of the cross section is $2-23$%, while the systematic uncertainty is in the range of $3.0-14.2$%. The results are consistent with previous measurements but have better accuracy.Comment: 13 pages, 11 figure

Study of the process e+e−→ηπ0γe^+e^- \to \eta\pi^0\gamma in the energy range \sqrt{s} = \mbox{1.05-2.00} GeV with the SND detector

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.Comment: 10 pages, 6 figures, to be submitted to European Physical Journal

Study of the process

The process $$e^+e^-\rightarrow \eta \eta \gamma$$ 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 $$e^+e^-\rightarrow \eta \eta \gamma$$ cross section is measured for the first time. It is shown that the dominant mechanism of this reaction is the transition through the $$\phi \eta$$ intermediate state. Our result on the $$e^+e^-\rightarrow \eta \eta \gamma$$ cross section is consistent with the $$e^+e^-\rightarrow \phi \eta$$ measurement in the $$\phi \rightarrow K^+ K^-$$ mode. The search for radiative processes contributing to the $$e^+e^-\rightarrow \eta \eta \gamma$$ cross section is performed, and no significant signal is observed

Measurement of the

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