Production of higher excited quarkonium pair at the super Z factory*

The heavy constituent quark pair of the heavy quarkonium is produced perturbatively and subsequently undergoes hadronization into the bound state non-perturbatively. The production of the heavy quarkonium is essential to testing our understanding of quantum chromodynamics (QCD) in both perturbative and non-perturbative aspects. The electron-positron collider will provide a suitable platform for the precise study of the heavy quarkonium. The higher excited heavy quarkonium may contribute significantly to the ground states, which should be considered for sound estimation. We study the production rates of the higher excited states quarkonium pair in ( - or b -quarks) at the future Z factory under the non-relativistic QCD (NRQCD) framework, where the / represents the color-singlet states , and ( ). The differential angle distribution of cross sections is given. We also discuss the uncertainties of cross sections caused by the varying quark masses and the renormalization scale μ . We show that significant numbers of events for pairs of higher excited state quarkonia can be generated at the super Z factory.