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Register a new userSearch for the decays $eta^{prime} to e^+e^-$ and $eta to e^+e^-$ at the VEPP-2000 $e^+e^-$ collider
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L.V. Kardapoltsev
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A search for the rare decay $eta^{prime} to e^+e^-$ has been performed with the SND detector at the VEPP-2000 $e^+e^-$ collider. The inverse reaction $e^+e^- to eta^{prime}$ and $eta^{prime}$ five decay chains have been used for this search. The upper limit $Gamma_{eta^{prime} to e^+e^-}<0.002$ eV at the 90% confidence level has been set. A sensitivity of SND in a search for $eta to e^+e^-$ decay has been studied. For this perpose we have analyzed a data sample with an integrated luminosity of 108 nb$^{-1}$ collected in the center-of-mass energy range 520-580 MeV. There are no background events for the reaction $e^+e^- to eta$ with decay $eta to pi^0pi^0pi^0$ have been found. In the absence of background, a sensitivity to $B(eta to e^+e^-)$ of 10$^{-6}$ can be reached during two weeks of VEPP-2000 operation.
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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 $etatopi^0pi^0pi^0$. 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.
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 $957.78pm 0.06$ MeV with an integrated luminosity of about 2.9 pb$^{-1}$. For reconstruction of the $eta^prime$ meson five decay chains have been used: $eta^{prime}toetapi^+pi^-$ followed by the $eta$ decays to $gammagamma$ and $3pi^0 $, and $eta^{prime} to etapi^0pi^0$ followed by the $eta$ decays to $pi^+pi^-pi^0$, $gammagamma$, and $3pi^0$. 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 process $e^+e^-{to}K^+K^-eta$ 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 $K^+K^-eta$ final state is found to be dominated by the contribution of the $phi(1020)eta$ intermediate state. The cross section of the process $e^+e^-{to}phi(1020)eta$ 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: $a_{mu}^{phieta}(E<1.8, {rm GeV})=(0.321 pm 0.015_{rm stat} pm 0.016_{rm syst}) times 10^{-10}$, $a_{mu}^{phieta}(E<2.0, {rm GeV})=(0.440 pm 0.015_{rm stat} pm 0.022_{rm syst}) times 10^{-10}$. From the cross section approximation the $phi(1680)$ meson parameters have been determined with better statistical precision, than in previous studies.
Based on a sample of etapr mesons produced in the radiative decay $J/psitogammaeta^{prime}$ in $1.31times 10^9$ $J/psi$ events collected with the BESIII detector, the decay $eta^{prime}toomega e^{+} e^{-}$ is observed for the first time, with a statistical significance of $8sigma$. The branching fraction is measured to be $mathcal{B}(eta^{prime}toomega e^{+} e^{-})=(1.97pm0.34(text{stat})pm0.17(text{syst}))times10^{-4}$, which is in agreement with theoretical predictions. The branching fraction of $eta^{prime}toomegagamma$ is also measured to be $(2.55pm0.03(text{stat})pm0.16(text{syst}))times10^{-2}$, which is the most precise measurement to date, and the relative branching fraction $frac{mathcal{B}(eta^{prime}to omega e^{+}e^{-})}{mathcal{B}(eta^{prime}to omega gamma)}$ is determined to be $(7.71pm1.34(text{stat})pm0.54(text{syst}))times10^{-3}$.
A search for the process $epemto eta^prime(958)$ in the $pipietatopipigammagamma$ final state has been performed with the CMD-3 detector at the VEPP-2000 $e^+e^-$ collider. Using an integrated luminosity of 2.69 pb$^{-1}$ collected at the center-of-mass energy Ecm = 957.68 MeV we set an upper limit for the product of electronic width and branching fractions $Gamma_{eta^prime(958)toepem}cdotBR_{eta^prime(958)topipieta}cdotBR_{etatogammagamma}<0.00041$ eV at 90% C.L.
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