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Register a new userObservation of $psi(3686) to eta e^+ e^- $
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Using a data sample of $448.1 times 10^6$ $psi(3686)$ events collected with the BESIII detector at the BEPCII collider, we report the first observation of the electromagnetic Dalitz decay $psi(3686) to eta e^+ e^-$, with significances of 7.0$sigma$ and 6.3$sigma$ when reconstructing the $eta$ meson via its decay modes $etatogamma pi^+ pi^-$ and $etatopi^+pi^-eta$ ($eta to gammagamma$), respectively. The weighted average branching fraction is determined to be $mathcal{B}(psi(3686) to eta e^+ e^-)= (1.90 pm 0.25 pm 0.11) times 10^{-6}$, where the first uncertainty is statistical and the second systematic.
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Using $4.479 times 10^{8}$ $psi(3686)$ events collected with the BESIII detector, we search for the decays $psi(3686) rightarrow e^{+}e^{-}chi_{c0,1,2}$ and $chi_{c0,1,2} rightarrow e^{+}e^{-}J/psi$. The decays $psi(3686) rightarrow e^{+}e^{-}chi_{c0,1,2}$ and $chi_{c0,1,2} rightarrow e^{+}e^{-}J/psi$ are observed for the first time. The measured branching fractions are $mathcal{B}(psi(3686) rightarrow e^{+}e^{-}chi_{c0,1,2}) = (11.7 pm 2.5 pm 1.0)times10^{-4}$, $(8.6 pm 0.3 pm 0.6)times10^{-4}$, $(6.9 pm 0.5 pm 0.6)times10^{-4}$, and $mathcal{B}(chi_{c0,1,2} rightarrow e^{+}e^{-}J/psi) = (1.51 pm 0.30 pm 0.13)times10^{-4}$, $(3.73 pm 0.09 pm 0.25)times10^{-3}$, $(2.48 pm 0.08 pm 0.16)times10^{-3}$. The ratios of the branching fractions $frac{mathcal{B}(psi(3686) rightarrow e^{+}e^{-}chi_{c0,1,2})}{mathcal{B}(psi(3686) rightarrow gammachi_{c0,1,2})}$ and $frac{mathcal{B}(chi_{c0,1,2} rightarrow e^{+}e^{-}J/psi)}{mathcal{B}(chi_{c0,1,2} rightarrow gamma J/psi)}$ are also reported.
Using the data samples of $(1310.6pm7.2 )times 10^{6}$ $J/psi$ events and $(448.1pm2.9)times 10^{6}$ $psi(3686)$ events collected with the BESIII detector, we search for the rare decays $J/psi to D^{0} e^{+}e^{-} +c.c.$ and $psi(3686) to D^{0} e^{+}e^{-} +c.c.$. No significant signals are observed and the corresponding upper limits on the branching fractions at the $90%$ confidence level are determined to be $Br(J/psi to D^{0} e^{+}e^{-} +c.c.)< 8.5times 10^{-8}$ and $Br (psi(3686) to D^{0} e^{+}e^{-} +c.c.)<1.4times 10^{-7}$, respectively. Our limit on $Br(J/psi to D^{0} e^{+}e^{-} +c.c.)$ is more stringent by two orders of magnitude than the previous results, and the $Br(psi(3686) to D^{0} e^{+}e^{-} +c.c.)$ is measured for the first time.
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 $(7.71pm1.34(text{stat})pm0.54(text{syst}))times10^{-3}$.
Using a 478 pb$^{-1}$ data sample collected with the BESIII detector operating at the BEPCII storage ring at a center-of-mass energy of $sqrt{s}=4.009$ GeV, the production of $e^{+}e^{-}to eta Jpsi$ is observed for the first time with a statistical significance of greater than $10sigma$. The Born cross section is measured to be $(32.1pm 2.8 pm 1.3)$ pb, where the first error is statistical and the second systematic. Assuming the $eta Jpsi$ signal is from a hadronic transition of the $psi(4040)$, the fractional transition rate is determined to be ${cal B}(psi(4040)to eta Jpsi)=(5.2pm 0.5pm 0.2pm 0.5)times 10^{-3}$, where the first, second, and third errors are statistical, systematic, and the uncertainty from the $psi(4040)$ resonant parameters, respectively. The production of $e^{+}e^{-} to pi^0 Jpsi$ is searched for, but no significant signal is observed, and ${cal B}(psi(4040)to pi^0 Jpsi) < 2.8 times 10^{-4}$ is obtained at the 90% confidence level.
We report the first observation of the Dalitz decay $eta to gamma e^+e^-$, based on a data sample of 1.31 billion $J/psi$ events collected with the BESIII detector. The $eta$ mesons are produced via the $J/psi to gamma eta$ decay process. The ratio $Gamma(eta to gamma e^+ e^-)/Gamma(etatogammagamma)$ is measured to be $(2.13pm0.09(text{stat.})pm0.07(text{sys.}))times10^{-2}$. This corresponds to a branching fraction ${cal B}(eta to gamma e^+e^-)= (4.69 pm0.20(text{stat.})pm0.23(text{sys.}))times10^{-4}$. The transition form factor is extracted and different expressions are compared to the measured dependence on the $e^+e^-$ invariant mass. The results are consistent with the prediction of the Vector Meson Dominance model.
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