Study Of J/ψ,ψ’→Ξ0Ξ0at BESⅢ

With226million J/ψ and106million ψ’ data samples collected by BESIII, both of which are the largest data samples in the world, we perform the careful studies of the processes J/ψ,ψ’→(?)0(?)0. According to the pair production feature of the processes, single tag of (?)0is used to reconstruct the signal events. Compared with the traditional method-full reconstruction of all the final states, this new method increases the event selection efficiency quite a lot and the backgrounds are still at an acceptable level. And the statistics of the signal events is improved significantly. Using the selected events J/ψ, ψ’→(?)0(?)0, the branching fractions are measured as The results are consistent with the previous measurement, but the precisions are improved. The Qh value, defined as B(ψ’→(?)0(?)0)/B(J/ψ’→(?)0(?)0),is determined to be (25.9±2.5)%, which enhanced somewhat compared with the12%role predicted by pQCD.Meanwhile, we also studied the angular distribution of (?)0in J/ψ’→(?)0(?)0which can be expressed as dN/d cos0α(1+αcos2θ). The parameters a are measured for the first time: This results satisfy the helicity selection rule and is consistent with the predic-tions.