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Register a new userEvidence for the Direct Two-Photon Transition from $psi(3686)$ to $J/psi$
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The two-photon transition $psi(3686)togammagamma J/psi$ is studied in a sample of 106 million $psi(3686)$ decays collected by the BESIII detector. The branching fraction is measured to be $(3.1pm0.6(unit{stat})^{+0.8}_{-1.0}(unit{syst})) times10^{-4}$ using $J/psito e^+e^-$ and $J/psitomu^+mu^-$ decays, and its upper limit is estimated to be $4.5times10^{-4}$ at the 90% conference level. This work represents the first measurement of a two-photon transition among charmonium states. The orientation of the $psi(3686)$ decay plane and the $J/psi$ polarization in this decay are also studied. In addition, the product branching fractions of sequential $E1$ transitions $psi(3686)togammachi_{cJ}, chi_{cJ}togamma J/psi (J=0,1,2)$ are reported.
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Motivated by a recent successful dynamical explanation for the newly observed fully-charm structure $X(6900)$ in the mass spectrum of di-$J/psi$ by LHCb [J.~Z.~Wang textit{et al.} arXiv:2008.07430], in this work, we extend the same dynamical rescattering mechanism to predict the line shape of more potential fully-heavy structures in the invariant mass spectrum of $J/psi psi(3686)$, $J/psi psi(3770)$, $psi(3686) psi(3686)$, and $J/psi Upsilon(1S)$ at high energy proton-proton collisions, whose verification in experiments should be helpful to further clarify the nature of $X(6900)$. The above final states of vector heavy quarkonia can be experimentally reconstructed more effectively by a $mu^+mu^-$ pair in the muon detector compared with $Qbar{Q}$ meson with other quantum numbers. Furthermore, the corresponding peak mass positions of each of predicted fully-heavy structures are also given. Our theoretical studies here could provide some valuable information for the future measurement proposals of LHCb and CMS, especially based on the accumulated data after completing Run III of LHC in the near future.
Using a data sample of $448.1times10^6$ $psi(3686)$ events collected with the BESIII detector operating at the BEPCII, we perform search for the hadronic transition $h_crightarrowpi^+pi^-J/psi$ via $psi(3686)rightarrowpi^0h_c$. No signals of the transition are observed, and the upper limit on the product branching fraction $mathcal{B}(psi(3686)rightarrowpi^0h_c)mathcal{B}(h_crightarrowpi^+pi^-J/psi)$ at the 90% confidence level is determined to be $2.0times10^{-6}$. This is the most stringent upper limit to date.
Using the data samples of $1.31times 10^9$ $J/psi$ events and $4.48times 10^8$ $psi(3686)$ events collected with the BESIII detector, partial wave analyses on the decays $J/psi$ and $psi(3686) to pi^+pi^-eta^prime$ are performed with a relativistic covariant tensor amplitude approach. The dominant contribution is found to be $J/psi$ and $psi(3686)$ decays to $rhoeta^prime$. In the $J/psi$ decay, the branching fraction ${cal B}(J/psito rhoeta^prime)$ is determined to be $(7.90pm0.19(mathrm{stat})pm0.49(mathrm{sys}))times 10^{-5}$. Two solutions are found in the $psi(3686)$ decay, and the corresponding branching fraction ${cal B}(psi(3686)to rhoeta^prime)$ is $(1.02pm0.11(mathrm{stat})pm0.24(mathrm{sys}))times 10^{-5}$ for the case of constructive interference, and $(5.69pm1.28(mathrm{stat})pm2.36(mathrm{sys}))times 10^{-6}$ for destructive interference. As a consequence, the ratios of branching fractions between $psi(3686)$ and $J/psi$ decays to $rhoeta^prime$ are calculated to be $(12.9pm1.4(mathrm{stat})pm3.1(mathrm{sys}))$% and $(7.2pm1.6(mathrm{stat})pm3.0(mathrm{sys}))$%, respectively. We also determine the inclusive branching fractions of $J/psi$ and $psi(3686)$ decays to $pi^+pi^-eta^prime$ to be $(1.36pm0.02(mathrm{stat})pm0.08(mathrm{sys}))times 10^{-4}$ and $(1.51pm0.14(mathrm{stat})pm 0.23(mathrm{sys}))times 10^{-5}$, respectively.
From $1310.6times10^{6}$ $J/psi$ and $448.1times10^{6}$ $psi(3686)$ events collected with the BESIII experiment, we report the first observation of $Sigma^{+}$ and $bar{Sigma}^{-}$ spin polarization in $e^+e^-rightarrow J/psi (psi(3686)) rightarrow Sigma^{+} bar{Sigma}^{-}$ decays. The relative phases of the form factors $DeltaPhi$ have been measured to be $(-15.5pm0.7pm0.5)^{circ}$ and $(21.7pm4.0pm0.8)^{circ}$ with $J/psi$ and $psi(3686)$ data, respectively. The non-zero value of $DeltaPhi$ allows for a direct and simultaneous measurement of the decay asymmetry parameters of $Sigma^{+}rightarrow p pi^{0}~(alpha_0 = -0.998pm0.037pm0.009)$ and $bar{Sigma}^{-}rightarrow bar{p} pi^{0}~(bar{alpha}_0 = 0.990pm0.037pm0.011)$, the latter value being determined for the first time. The average decay asymmetry, $(alpha_{0} - bar{alpha}_{0})/2$, is calculated to be $-0.994pm0.004pm0.002$. The CP asymmetry $A_{rm CP,Sigma} = (alpha_0 + bar{alpha}_0)/(alpha_0 - bar{alpha}_0) = -0.004pm0.037pm0.010$ is extracted for the first time, and is found to be consistent with CP conservation.
Using 106~million $psi(3686)$ events collected with the BESIII detector, we measure multipole amplitudes for the decay $psi(3686)rightarrowgammachi_{c1,2}togammagamma J/psi$ beyond the dominant electric-dipole amplitudes. The normalized magnetic-quadrupole amplitude for $psi(3686)rightarrowgammachi_{c1,2}rightarrowgammagamma J/psi$ and the normalized electric-octupole amplitudes for $psi(3686)rightarrowgammachi_{c2}$,~$chi_{c2}rightarrowgamma J/psi$ are determined. The M2 amplitudes for $psi(3686)rightarrowgammachi_{c1}$ and $chi_{c1,2}rightarrowgamma J/psi$ are found to differ significantly from zero and are consistent with theoretical predictions. We also obtain the ratios of M2 contributions of $psi(3686)$ and $J/psi$ decays to $chi_{c1,2}$, $b_{2}^{1}/b_{2}^{2} = 1.35pm0.72$ and $a_{2}^{1}/a_{2}^{2} = 0.617pm0.083$, which agree well with theoretical expectations. By considering the multipole contributions of $chi_{c1,2}$, we measure the product branching fractions for the cascade decays $psi(3686)rightarrowgammachi_{c0,1,2}togammagamma J/psi$ and search for the process $eta_{c}(2S)togamma J/psi$ through $psi(3686)rightarrowgammaeta_{c}(2S)$. The product branching fraction for $psi(3686)rightarrowgammachi_{c0}togammagamma J/psi$ is 3$sigma$ larger than published measurements, while those of $psi(3686)rightarrowgammachi_{c1,2}togammagamma J/psi$ are consistent. No significant signal for the decay $psi(3686)togamma eta_c(2S)togamma gamma J/psi$ is observed, and the upper limit of the product branching fraction at the 90% confidence level is determined.
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