Recent Charmonium Physics from BES

TL;DR

This paper reports comprehensive measurements of charmonium states, including branching fractions, decay modes, cross sections, and mass and width determinations, based on extensive BES detector data, advancing understanding of charmonium physics.

Contribution

It provides new measurements of branching fractions, decay modes, and properties of charmonium states using large BES datasets, including first observations of certain decay channels.

Findings

Measured branching fractions for nine final states.

Determined mass and width of eta_c.

First observation of chicJ decays to lambda lambda-bar.

Abstract

Measurements of branching fractions for nine different final states, based on a data sample of approximately 4 million psi(2S) events collected with the BESI detector at the BEPC, are reported. Using the same event sample, radiative decays of the psi (2S) into pi pi, K K-bar and eta eta final states have been measured. Cross sections for e e -> e e, hadrons, pi pi J/psi, and mu mu have been measured in the vicinity of the psi(2S) resonance using the BESII detector. The psi(2S) total width; partial widths to hadrons, pi pi J/psi and muons; and corresponding branching fractions have been determined. Decays of J/psi -> gamma eta_c are used to determine the mass and width of the eta_c using a sample of 58 M J/psi events. $M_{\eta_c} = (2977.5 \pm 1.0 \pm 1.2)$ MeV and $\Gamma_{\eta_c} = (17.0 \pm 3.7 \pm 7.4)$ MeV. The first observation of chicJ (J=0,1,2) decays to lambda lambda-bar is reported using psi(2S) data collected with the BESII detector. Results are compared with model predictions.