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Register a new userMeasurement of $mathcal{B}(J/psi to eta e^+ e^- $) and search for a dark photon
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Using a data sample of $(1310.6pm7.0)times10^{6}$ $J/psi$ decay events collected with the BESIII detector at BEPCII, we study the electromagnetic Dalitz decay $J/psi to eta e^+e^-$ with two dominant $eta$ decay modes, $eta to gamma pi^+ pi^-$ and $eta to pi^+pi^-eta$. The branching fraction is determined to be $mathcal{B}(J/psi to eta e^+e^-) = (6.59pm0.07pm0.17) times 10^{-5}$, which improves in precision by a factor of 2 over the previous BESIII measurement. A search for the dark photon ($gamma $) is performed via $J/psi toeta gamma , gamma to e^{+}e^{-}$. Excluding the $omega$ and $phi$ mass regions, no significant signal is observed in the mass range from 0.1 to 2.1 GeV/$c^{2}$. We set upper limits at the 90% confidence level on $mathcal{B}(J/psi to eta gamma )timesmathcal{B}(gamma to e^+e^-)$, $mathcal{B}(J/psi toeta gamma$) and the mixing strength as a function of dark photon mass. This is among the first searches for dark photons in charmonium decays.
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Using data samples collected with the BESIII detector operating at the BEPCII collider at center-of-mass energies from 3.810 to 4.600 GeV, we perform a study of $e^{+}e^{-} to eta J/psi$ and $pi^0 J/psi$. Statistically significant signals of $e^{+}e^{-} to eta J/psi$ are observed at $sqrt{s}$ = 4.190, 4.210, 4.220, 4.230, 4.245, 4.260, 4.360 and 4.420 GeV, while no signals of $e^{+}e^{-} to pi^{0} J/psi$ are observed. The measured energy-dependent Born cross section for $e^{+}e^{-} to eta J/psi$ shows an enhancement around 4.2~GeV. The measurement is compatible with an earlier measurement by Belle, but with a significantly improved precision.
We have measured several branching ratios for $psi^prime$ decay using the data collected by FNAL E835 experiment during year 2000, obtaining ${cal B}(psi^prime to e^+ e^-) = 0.0068pm0.0001pm0.0004$, ${cal B}(psi^prime to J/psi pi^+ pi^-) = 0.292pm0.005pm0.018$, ${cal B}(psi^prime to J/psi pi^0 pi^0) = 0.167pm0.005pm0.014$ and ${cal B}(psi^prime to J/psi eta) = 0.028pm0.002pm0.002$. We also present a measurement of the dipion mass distribution in the decays $psi^prime to J/psi pi pi$.
Using a data sample of $448.1times10^6$ $psi(3686)$ events collected at $sqrt{s}=$ 3.686 GeV with the BESIII detector at the BEPCII, we search for the rare decay $J/psi to phi e^+ e^-$ via $psi(3686) to pi^+pi^- J/psi $. No signal events are observed and the upper limit on the branching fraction is set to be $mathcal{B}(J/psi to phi e^+ e^-) < 1.2 times 10^{-7}$ at the 90% confidence level, which is still about one order of magnitude higher than the Standard Model prediction.
We study the electromagnetic Dalitz decay $J/psi to e^+e^- eta$ and search for di-electron decays of a dark gauge boson ($gamma$) in $J/psi to gamma eta$ with the two $eta$ decay modes $eta rightarrow gamma gamma$ and $eta rightarrow pi^+pi^-pi^0$ using $(1310.6pm 7.0)times10^6$ $J/psi$ events collected with the BESIII detector. The branching fraction of $J/psi to e^+e^- eta$ is measured to be $(1.43 pm 0.04 ({rm stat}) pm 0.06 ({rm syst}))times 10^{-5}$, with a precision that is improved by a factor of $1.5$ over the previous BESIII measurement. The corresponding di-electron invariant mass dependent modulus square of the transition form factor is explored for the first time, and the pole mass is determined to be $Lambda = 2.84 pm 0.11({rm stat}) pm 0.08({rm syst})$ GeV/$c^2$. We find no evidence of $gamma$ production and set $90%$ confidence level upper limits on the product branching fraction $mathcal{B}(J/psi to gamma eta)times mathcal{B}(gamma to e^+e^-)$ as well as the kinetic mixing strength between the Standard Model photon and $gamma$ in the mass range of $0.01 le m_{gamma} le 2.4$ GeV/$c^2$.
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.
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