NLO QCD corrections to exclusive quarkonium-pair production in photon–photon collision Hao Yang, Zi-Qiang Chen and Cong-Feng Qiao Eur. Phys. J. C, 80 9 (2020) 806 Published online: 01 September 2020 DOI: 10.1140/epjc/s10052-020-8390-z