No Arabic abstract
Using 58 million $J/psi$ and 14 million $psi(2S)$ events collected by the BESII detector at the BEPC, branching fractions or upper limits for the decays $J/psi$ and $psi(2S) to Lambda bar{Lambda} pi^0$ and $Lambda bar{Lambda} eta$ are measured, and the decays of $J/psi$ and $psi(2S)$ to $n K^0_S bar{Lambda}+c.c.$ are observed and measured for the first time. Finally, $R$ measurement data taken with the BESII detector at center-of-mass energies between 3.7 and 5.0 GeV are fitted to determine resonance parameters of the high mass charmonium states, $psi(3770)$, $psi(4040)$, $psi(4160)$, and $psi(4415)$. The Beijing Electron Collider is being upgraded to a two-ring collider (BEPCII) with a design luminosity of $1 times 10^{33}$cm$^{-2}$ s$^{-1}$ at 3.89 GeV and will operate between 2 and 4.2 GeV in the center of mass. With this luminosity, the new BESIII detector will beable to collect, for example, 10 billion $J/psi$ events in one year of running. BEPCII and BESIII are currently nearing completion, and commissioning of both is expected to begin in mid-2008.
We report the preliminary R values for all the 85 energy points scanned in the energy region of 2-5 GeV with the upgraded Beijing Spectrometer (BESII) at Beijing Electron Positron Collider (BEPC). Preliminary results from the J/psi data collected with both BESI and BESII are presented. Measurements of the branching fraction of the psi(2S) decays and the psi(2S) resonance parameters are reported. The future plans, i.e. significantly upgrade the machine and detector are also discussed.
BESIII experiment has collected about 20 fb$^{-1}$ luminosity data between $sqrt{s}=3.8$ and 4.7 GeV via $e^{+}e^{-}$ collision. In this talk, we present the recent $XYZ$ results at BESIII, including mass and width measurements of $Y(4220)$, search for $Y$ states with rare decay modes, isospin parity determination of $Z_{c}^{0}(3900)$ as well as the mass and width determination, and search for new decay modes of $X(3872)$.
Hadron spectroscopy is one of the most important physics goals of BESIII. BESIII brings great opportunities to study the XYZ states of charmonium by directly producing the Y states up to 4.6 GeV. High statistics of charmonium decays collected at BESIII provide an excellent place for hunting gluonic excitations and studying the excited baryons. Recent results of light hadron spectroscopy and charmonium spectroscopy from BESIII will be reported.
There are about 33, 6.5 and 1.0 pb$^{-1}$ of $e^+e^-$ annihilation data have been taken around the center-of-mass energies of $sqrt s=$ 3.773 GeV, at $sqrt s=$ 3.650 GeV and at $sqrt s=$ 3.6648 GeV, respectively, with the BES-II detector at the BEPC collider. By analyzing these data sets, we have measured the branching fraction for $psi(3770)to$ non-$Dbar D$ by several different methods; and have observed an anomalous line shape of $sigma^{e^+e^-to{rm hadrons}}$ in energy region from 3.65 to 3.87 GeV; and have measured the line shapes of the $D^+D^-$, $D^0bar D^0$ and $Dbar D$ production and together with the ratios of the production rates of $D^+D^-$ and $D^0bar D^0$ in $e^+e^-$ annihilation around the $psi(3770)$ resonance.
We have updated our evaluation of the hadronic contribution to the running of the QED fine structure constant using the recent precise measurements of the e+e- annihilation at the center-of-mass (c.m.s.) energy region between 2.6 and 3.65 GeV performed by the BES collaboration. In the low energy region, around the rho resonance, we include the recent measurements from the BABAR, CDM-2, KLOE and SND collaborations. We obtain Delta alpha (5)_had (s) = 0.02750 +/- 0.00033 at s = m_Z^2.