Recent BES results and the BESIII upgrade

Abstract

Using 58 million $J/ψ$ and 14 million $ψ(2S)$ events collected by the BESII detector at the BEPC, branching fractions or upper limits for the decays $J/ψ$ and $ψ(2S) \to Λ\barΛ π^0$ and $Λ\barΛ η$ are measured, and the decays of $J/ψ$ and $ψ(2S)$ to $n K^0_S \barΛ+c.c.$ 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, $ψ(3770)$, $ψ(4040)$, $ψ(4160)$, and $ψ(4415)$. 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 $J/ψ$ events in one year of running. BEPCII and BESIII are currently nearing completion, and commissioning of both is expected to begin in mid-2008.