Recent BES results and the BESIII upgrade

TL;DR

This paper reports recent BES results on charmonium decays, measurements of resonance parameters, and discusses the upgrade of the BEPC collider to BESIII, enabling large data collection for future studies.

Contribution

It provides new measurements of decay branching fractions, observes new decay modes, and determines resonance parameters with the upgraded BESIII detector and BEPCII collider.

Findings

Measured branching fractions and upper limits for specific decays.

First observation and measurement of certain decay modes.

Determined resonance parameters of high mass charmonium states.

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.