Study Of The Charmonium States χ_cJ And ψ（4415） At BESⅢ

Charmonium systems provide a unique laboratory to study the interplay between perturbative and non-perturbative effects in quantum chromodynamics.Experimental studies of charmonium exclusive decays are of special importance for a better understanding of their nature and decay mechanism.Based on 448.1 × 106 ty(3686)events collected with the BESⅢ detector operated on BEPCII,the two-photon and hadronic decays of χcJ are studied via the E1 radiative transition ψ(3686)→γχcJ.Based on the measurements of the branching factions ofχc0,2 →γγ the ratio of the partial widths of the two-photon decays χc2 and χc0 are determined to be R=Γγγ(χc2)/Γγγ(χc0)=0.295±0.014±0.007±0.027,where the first uncertainty is statistical,the second one is systematic and the third one is associated with the uncertainties of B(ψ(3686)→γχc0,2)and the total widths Γ(χc0,2).This is the most precise measurement to date.The measured value is consistent with previous measurements but higher than the first order theoretical prediction,which may indicate the high order theoretical calculations are needed to explain the experimental observation;The decay χc1→γγ is theoretically forbidden by the Landau-Yang theorem.No signal of such decay is observed experimentally.The upper limits at the 90%confidence level on the two-photon partial width is set;A helicity amplitude analysis for the decay of ψ(3686)→γχc2,χc2→γγ is performed.The ratio of the two-photon partial widths between the helicity-zero and helicity-two components is determined to be f0/2=Γγγλ=0(χc2)/Γγγλ=2(χc2)=(0.0±0.6±1.2)× 10-2,confirming that helicity-zero component is highly suppressed;For the hadronic decay χcJ →φφη,the branching fractions are measured for the first time.Compared to the pure phase space decays,some excesses are observed in the invariant masses spectra of φφ and φη.Future studies with more data are needed to make clear conclusions.The ψ(4415)particle is predicted to be the 4S state of the cc quarkonia.It may decay to ten open-charm final states.Precise measurement of its mass and width are important for testing the potential model.Using data samples collected with BESⅢ detector at 28 different center-of-mass energies from 4.340 GeV to 4.600 GeV,the cross sections of e+e-→D2*(2460)D→D0D-π++c.c.are measured.The decay of e+e-→D0D-π+c.c.is found to be dominated by e+e-→D2*(2460)D.Based on the measured ineshape of the cross sections,the mass and full width of ψ(4415)are determined.The mass is consistent with the non-relativistic potential model prediction.