ATLAS collaboration (2854 authors)Aguilar-Saavedra, Juan AntonioAmor Dos Santos, Susana PatriciaAnjos, NunoAraque, Juan PedroCarvalho, JoãoCastro, Nuno FilipeConde Muiño, PatriciaDa Cunha Sargedas De Sousa, Mario JoseFiolhais, MiguelGalhardo, BrunoGomes, AgostinhoGonçalo, RicardoJorge, PedroMachado Miguens, JoanaMaio, AméliaManeira, JoséOleiro Seabra, Luis FilipeOnofre, AntónioPedro, RuteSantos, HelenaSaraiva, JoãoSilva, JoséTavares Delgado, AdemarVeloso, FilipeWolters, Helmut2019-02-042019-02-042017-02-07http://dx.doi.org/10.1140/epjc/s10052-017-4644-9http://hdl.handle.net/10400.26/27250The production of two prompt $J/\psi $ mesons, each with transverse momenta $p_{\mathrm {T}}>8.5$  GeV and rapidity $|y| < 2.1$ , is studied using a sample of proton-proton collisions at $\sqrt{s} = 8$  TeV, corresponding to an integrated luminosity of 11.4 fb$^{-1}$ collected in 2012 with the ATLAS detector at the LHC. The differential cross-section, assuming unpolarised $J/\psi $ production, is measured as a function of the transverse momentum of the lower- $p_{\mathrm {T}}$ $J/\psi $ meson, di- $J/\psi $ $p_{\mathrm {T}}$ and mass, the difference in rapidity between the two $J/\psi $ mesons, and the azimuthal angle between the two $J/\psi $ mesons. The fraction of prompt pair events due to double parton scattering is determined by studying kinematic correlations between the two $J/\psi $ mesons. The total and double parton scattering cross-sections are compared with predictions. The effective cross-section of double parton scattering is measured to be $\sigma _{\mathrm {eff}} = 6.3 \pm 1.6 \mathrm {(stat)} \pm 1.0 \mathrm {(syst)}$  mb.engjournal article2019-02-04