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Some recent progress in understanding exclusive double charmonium production at $B$ factories

We review some recent progress in understanding various exclusive double charmonium production processes at $B$ factories, within the nonrelativistic QCD factorization framework. First we investigate the impact of the joint perturbative and relativistic correction on the process that has attracted a great amount of attention in the past decade, $e^+e^-\to J/ψ+η_c$. We then briefly discuss the phenomenological implication of the next-to-leading order perturbative correction to the processes $e^+e^-\to J/ψ+χ_{c0,1,2} (η_{c2})$. We further emphasize a novel theoretical challenge, which is recently discovered by applying the NRQCD factorization approach to the helicity-suppressed hard exclusive reactions involving heavy quarkonium.