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Register a new userObservation of Electromagnetic Dalitz decays J/psi to P e^+e^-
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M. Ablikim
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Based on a sample of (225.3pm2.8)times 10^{6} J/psi events collected with the BESIII detector, the electromagnetic Dalitz decays of J/psi to P e^+e^-(P=eta/eta/pi^0) are studied. By reconstructing the pseudoscalar mesons in various decay modes, the decays J/psi to eta e^+e^-, J/psi to eta e^+e^- and J/psi to pi^0 e^+e^- are observed for the first time. The branching fractions are determined to be mathcal{B}(J/psito eta e^+e^-) = (5.81pm0.16pm0.31)times10^{-5}, mathcal{B}(J/psito eta e^+e^-) = (1.16pm0.07pm0.06)times10^{-5}, and mathcal{B}(J/psito pi^0 e^+e^-)=(7.56pm1.32pm0.50)times10^{-7}, where the first errors are statistical and the second ones systematic.
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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/$c^2$.
We study the $e^+e^-togammaomega J/psi$ process using $11.6 ~rm fb^{-1}$ $e^+ e^-$ annihilation data taken at center-of-mass energies from $sqrt{s}=4.008~rm GeV$ to $4.600~rm GeV$ with the BESIII detector at the BEPCII storage ring. The $X(3872)$ resonance is observed for the first time in the $omega J/psi$ system with a significance of more than $5sigma$. The relative decay ratio of $X(3872)toomega J/psi$ and $pi^+pi^- J/psi$ is measured to be $mathcal{R}=1.6^{+0.4}_{-0.3}pm0.2$, where the first error is statistical and the second systematic (the same hereafter). The $sqrt{s}$-dependent cross section of $e^+e^-togamma X(3872)$ is also measured and investigated, and it can be described by a single Breit-Wigner resonance, referred to as the $Y(4200)$, with a mass of $4200.6^{+7.9}_{-13.3}pm3.0~{rm MeV}/c^2$ and a width of $115^{+38}_{-26}pm12~{rm MeV}$. In addition, to describe the $omega J/psi$ mass distribution above $3.9~rm GeV/c^2$, we need at least one additional Breit-Wigner resonance, labeled as $X(3915)$, in the fit. The mass and width of the $X(3915)$ are measured to be $3926.4pm2.2pm1.2~rm MeV/c^2$ and $3.8pm7.5pm2.6~rm MeV$, or $3932.6pm8.7pm4.7~rm MeV/c^2$ and $59.7pm15.5pm3.7~rm MeV$, respectively, depending on the fit models. The resonant parameters of the $X(3915)$ agree with those of the $Y(3940)$ in $Bto Komega J/psi$ and of the $X(3915)$ in $gammagammatoomega J/psi$ by the Belle and BABAR experiments within errors.
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.
Using a sample of $2.25times 10^8$ $J/psi$ events collected with the BESIII detector at the BEPCII collider, we search for the $J/psi$ semi-leptonic weak decay $J/psi to D^{-}_{s} e^{+} u_{e}+c.c.$ with a much higher sensitivity than previous searches. We also perform the first search for $J/psi to D^{*-}_{s} e^{+} u_{e}+c.c.$ No significant excess of a signal above background is observed in either channel. At the $90%$ confidence level, the upper limits are determined to be $mathcal{B}(J/psi to D^{-}_{s}e^{+} u_{e}+c.c.)<1.3times10^{-6}$ and $mathcal{B}(J/psi to {D^{*}_{s}}^{-}e^{+} u_{e}+c.c.)<1.8times10^{-6}$, respectively. Both are consistent with Standard Model predictions.
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