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Register a new userObservation of the $Y(4220)$ and $Y(4360)$ in the process $e^{+}e^{-} to eta J/psi$
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The cross sections of the process $e^{+}e^{-} to eta J/psi$ at center-of-mass energies ($sqrt{s}$) between 3.81 and 4.60 GeV are measured with high precision by using data samples collected with the BESIII detector operating at the BEPCII storage ring. Three structures are observed by analyzing the lineshape of the measured cross sections, and a maximum-likelihood fit including three resonances is performed by assuming the lowest lying structure is the $psi(4040)$. For the other resonances, we obtain masses of $(4218.7 pm 4.0 pm 2.5)$ and $(4380.4 pm 14.2 pm 1.8)$ MeV/c$^{2}$ with corresponding widths of $(82.5 pm 5.9 pm 0.5)$ and $(147.0 pm 63.0 pm 25.8)$ MeV, respectively, where the first uncertainties are statistical and the second ones systematic. The measured resonant parameters are consistent with those of the $Y(4220)$ and $Y(4360)$ from pr evious measurements of different final states. For the first time, we observe the decays of the $Y(4220)$ and $Y(4360)$ into $eta J/psi$ final states.
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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.
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 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 $psi^prime to J/psi pi pi$.
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.
The state $Y(2175)$ is observed in the process $e^+ e^- to eta Y(2175)$ at center-of-mass energies between 3.7 and 4.6$sim$GeV with a statistical significance larger than $10sigma$ using data collected with the BESIII detector operating at the BEPCII storage ring. This is the first observation of the $Y(2175)$ in this process. The mass and width of the $Y(2175)$ are determined to be ($2135pm 8pm 9$)~MeV/$c^2$ and ($104pm 24pm 12$)~MeV, respectively, and the production cross section of $e^+ e^- to eta Y(2175)to etaphi f_{0}(980)to etaphi pi^+ pi^-$ is at a several hundred femtobarn level. No significant signal for the process $e^+ e^- to eta Y(2175)$ is observed and the upper limit on $sigma(e^+ e^- to eta Y(2175))/sigma(e^+ e^- to eta Y(2175))$ is estimated to be 0.43 at the 90% confidence level. We also search for $psi(3686) to eta Y(2175)$. No significant signal is observed, indicating a strong suppression relative to the corresponding $J/psi$ decay, in violation of the 12% rule.
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