Analysis Of Several Questions In ψ (2S) Decay On BESIII

Since the cc bound state of J/ψhad been discovered, the charmonium family have been subsequently discovered in experiment, such asψ(2S),ψ(3770), and so on. As one of the important members of the family,χcJ is very important for us to study the violation mech-anism of helicity. According to the earlier QCD analysis of charmonium hardronic decays, it argued that if the quark masses are neglected in the gluonic hardronization processes, then the helicity conservation leads to a simple helicity selection rule, which states that a spin-0 particle cannot be allowed to decay into two fermions with opposite helicities along the baryonic outgoing direction. Thus it immediately forbids the decayχc0→pp-How-ever, the experimental value for the decay is (2.15±0.19)×10-4[2]. Although the value is small, the largeψ(2S) events at BESIII is helpful for us to study the hardronic decay of XcJ.In this paper, we analyse the joint angle distribution of the particles of the de-cay e+e-ψ(2S)→γχcJ→γ(?)(?)→γpπ-pπ+ to their mother particle rest frame, and the sensitivities for the measuring decay parameter of A(A) are calculated.As another important member of charmonium,hc(1Pi) has been predicted in theory for many years. The decayψ(2S)→π0hc and hc→γηc have played a crucial role in the understanding of QCD theory and charmonium. But both the branching ratios of the two decay channels have not been measured yet. With the events ofψ(2S), we measured the mass of hc, the branching ratios ofψ(2S)→π0hc and hc→γηc, the joint branching ratio of the two channels is also included in this paper. Among these results, the branching ratios ofψ(2S)→π0hc and hc→γηc are the first measurement in the world.At last, we measure the branching ratio ofψ(2S)→π0(η)J/ψso as to do something helpful for the testing of the ratio of quark mu/md, and the result is also helpful to understand CP violation.