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Register a new userCombined fit to the cross sections of $e^+e^- rightarrow pi Z_c(3900) rightarrow pipi J/psi$ and $e^+e^- rightarrow pi Z_c(3900) rightarrow pi Dbar{D}^{*}$
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The cross sections of $e^+e^- rightarrow pi Z_c(3900) rightarrow pipi J/psi$ and $e^+e^- rightarrow pi Z_c(3900) rightarrow pi Dbar{D}^{*}$ have been measured by BESIII experiment. We try to perform a combined fit to the cross sections with one Breit-Wigner function, the fit results show the structures mass and width are $M=(4232pm5)$ MeV/$c^2$, $Gamma=(65pm21)$ MeV. The ratio $frac{mathcal{B}(Z_c(3900)rightarrow Dbar{D}^{*})}{mathcal{B}(Z_c(3900)rightarrowpi J/psi)}$ is determined to be $(16pm6)$. We also try to fit the cross sections with two Breit-Wigner functions, while we cant come to any definitive conclusions about the second structure. More measurements are desired to improve the understanding of $e^+e^- rightarrow pi Z_c(3900)$ line shape.
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Using data samples collected with the BESIII detector operating at the BEPCII storage ring at center-of-mass energies from 4.178 to 4.600 GeV, we study the process $e^+e^-rightarrowpi^{0}X(3872)gamma$ and search for $Z_c(4020)^{0}rightarrow X(3872)gamma$. We find no significant signal and set upper limits on $sigma(e^+e^-rightarrowpi^{0}X(3872)gamma)cdotmathcal{B}(X(3872)rightarrowpi^{+}pi^{-}J/psi)$ and $sigma(e^+e^-rightarrowpi^{0}Z_c(4020)^{0})cdotmathcal{B}(Z_c(4020)^{0}rightarrow X(3872)gamma)cdotmathcal{B}(X(3872)rightarrowpi^{+}pi^{-}J/psi)$ for each energy point at $90%$ confidence level, which is of the order of several tenths pb.
We study e+e- --> pi+pi-h_c at center-of-mass energies from 3.90 GeV to 4.42 GeV using data samples collected with the BESIII detector operating at the Beijing Electron Positron Collider. The Born cross sections are measured at 13 energies, and are found to be of the same order of magnitude as those of e+e- --> pi+pi-J/psi but with a different line shape. In the pi^pm h_c mass spectrum, a distinct structure, referred to as Z_c(4020), is observed at 4.02 GeV/c^2. The Z_c(4020) carries an electric charge and couples to charmonium. A fit to the pi^pm h_c invariant mass spectrum, neglecting possible interferences, results in a mass of (4022.9pm 0.8pm 2.7) MeV/c^2 and a width of (7.9pm 2.7pm 2.6) MeV for the Z_c(4020), where the first errors are statistical and the second systematic. No significant Z_c(3900) signal is observed, and upper limits on the Z_c(3900) production cross sections in pi^pm h_c at center-of-mass energies of 4.23 and 4.26 GeV are set.
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.
Several intermediate states of the reaction channels $e^{+}e^{-} rightarrow pi^{+} pi^{-} D^{0} bar{D}^{0}$ and $e^{+}e^{-} rightarrow pi^{+} pi^{-} D^{+}D^{-}$ are studied using the data samples collected with the BESIII detector at center-of-mass energies above 4.08 GeV. For the first time in this final state, a $psi(3770)$ signal is seen in the $Dbar{D}$ invariant mass spectrum, with a statistical significance of $5.2sigma$ at $sqrt{s} = 4.42$ GeV. There is also evidence for this resonance at $sqrt{s}$ = 4.26 and 4.36 GeV with statistical significance of 3.2$sigma$ and 3.3$sigma$, respectively. In addition, the Born cross section of $e^{+}e^{-}to pi^{+}pi^{-}psi(3770)$ is measured. The proposed heavy-quark-spin-symmetry partner of the $X(3872)$, the state $X_{2}(4013)$, is also searched for in the $Dbar{D}$ invariant mass spectra. No obvious signal is found. The upper limit of the Born cross section of the process $e^{+}e^{-}to rho^{0}X_{2}(4013)$ combined with the branching fraction is measured. Also, the processes $e^{+}e^{-}to D_{1}(2420)bar{D} + c.c.$ are investigated. The neutral mode with $D_{1}(2420)^{0}to D^{0}pi^{+}pi^{-}$ is reported with statistical significance of 7.4$sigma$ at $sqrt{s} = 4.42$ GeV for the first time, and evidence with statistical significance of 3.2$sigma$ and 3.3$sigma$ at $sqrt{s}$ = 4.36 and 4.60 GeV is seen, respectively. No evident signal for the process $e^{+}e^{-}to D_{1}(2420)^{0}bar{D}^{0} + c.c., D_{1}(2420)^{0}to D^{*+}pi^{-}$ is reported. Evidence for $e^{+}e^{-}to D_{1}(2420)^{+}D^{-} +~c.c., D_{1}(2420)^{+}to D^{+}pi^{+}pi^{-}$ is reported with statistical significance of 3.1$sigma$ and 3.0$sigma$ at $sqrt{s}$ = 4.36 and 4.42 GeV, respectively.
We present the first measurements of branching fractions of rare tau-lepton decays, $tau^- rightarrow pi^- u_{tau} ell^+ ell^-$ ($ell = e$ or $mu$), using a data sample corresponding to 562 fb$^{-1}$ collected at a center-of-mass energy of 10.58 GeV with the Belle detector at the KEKB asymmetric-energy $e^+ e^-$ collider. The $tau^- rightarrow pi^- u_tau e^+ e^-$ decay is observed for the first time with 7.0$sigma$ significance. The partial branching fraction determined by the structure-dependent mechanisms mediated by either a vector or an axial-vector current for the mass region $M_{pi e e}>1.05$ GeV/$c^2$ is measured to be $mathcal{B}(tau^-rightarrow pi^- u_tau e^+ e^-)[M_{pi^- e^+ e^-}>1.05~{rm GeV}/c^2] = (5.90 pm 0.53 pm 0.85 pm 0.11) times 10^{-6}$, where the first uncertainty is statistical, the second is systematic, and the third is due to the model dependence. In the full phase space, due to the different detection efficiencies for the structure-dependent mechanisms mediated by axial-vector and vector currents, the branching fraction varies from $mathcal{B}_{A}(tau^-rightarrow pi^- u_tau e^+ e^-) = (1.46 pm 0.13 pm 0.21) times 10^{-5}$ to $mathcal{B}_{V}(tau^-rightarrow pi^- u_tau e^+ e^-) = (3.01 pm 0.27 pm 0.43) times 10^{-5}$, respectively. An upper limit is set on the branching fraction of the $tau^- rightarrow pi^- u_tau mu^+ mu^-$ decay, $mathcal{B}(tau^-rightarrow pi^- u_tau mu^+ mu^-) < 1.14 times 10^{-5}$, at the 90% confidence level.
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