Next-to-leading-order relativistic and QCD corrections to prompt J/ pair photoproduction at future e^+e^- colliders

Within the framework of nonrelativistic-QCD factorization, we calculate both the next-to-leading-order relativistic and QCD corrections to prompt J/ pair production, with feeddown from (2S) mesons, via photon-photon collisions at future e^+e^- colliders including the Future Circular Lepton Collider (FCC-ee), the Circular Electron Positron Collider (CEPC), and the Compact Linear Collider (CLIC). We present total cross sections and distributions in single J/ transverse momentum and rapidity, and in J/ pair invariant mass. The relativistic and QCD corrections both turn out to be large and negative. Yet, the production rates are large enough for useful experimental studies.