The Study Of Charmonium Transition At BESâ…¢

Charmonium physics has played an important role to understand Quantum Chro-modynamics (QCD), because charmonium states are expected to be far less affected by the problems associated with relativistic effects and the large value of the strong coupling constant αs. In the QCD potential model, the spin-independent one-gluon exchange part of the qq interaction have been defined quite well by the existing experi-mental data. But the spin dependence of the qq potential, particularly for the spin-spin interaction, is not well understood because of limited experimental data. Until now, the only hyperfine splitting known was that for the15states of charmonium, ΔMhf(1S)=M(J/ψ)-M(ηc)=117±1MeV. Recently, BaBar, Belle, CLEO and BESⅢ suc-ceeded in identifying ηc(2S), with result ΔMhf(2S)=M(ψ(2S))-M(ηc(2S))=49±4MeV.In the charmonium family, the observation of the hc is important because a com-parison of its mass with the masses of the3P states provides information on the spin dependence of the qq interaction. According to QCD potential models, the Coulom-bic vector potential arising from one-gluon exchange between the quark and the an-tiquark produces hyperfine splitting only for S states. This leads to the prediction of the hyperfine or triplet-singlet splitting in the P states of Mhf≡<M(13P)>-M(11P1)(?)0。The current experimental value of spin-weighted average mass of3P states...