The production of two prompt J/ ψ mesons, each with transverse momenta pT> 8.5 GeV and rapidity |y| < 2.1 , is studied using a sample of proton-proton collisions at 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/ ψ production, is measured as a function of the transverse momentum of the lower-pTJ/ ψ meson, di-J/ ψpT and mass, the difference in rapidity between the two J/ ψ mesons, and the azimuthal angle between the two J/ ψ mesons. The fraction of prompt pair events due to double parton scattering is determined by studying kinematic correlations between the two J/ ψ 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 σeff= 6.3 ± 1.6 (stat) ± 1.0 (syst) mb.

Measurement of the prompt J/ ψ pair production cross-section in pp collisions at √s=8 TeV with the ATLAS detector

Amoroso, S.;Barbero, M.;Bellagamba, L.;Benitez, J.;Bona, M.;Cairo, V. M.;Callea, G.;Cao, T.;Capua, M.;Cardillo, F.;Carli, I.;Cavaliere, V.;Cerri, A.;Chen, H.;Chiarella, V.;Colombo, T.;Conti, G.;Crosetti, G.;David, C.;De Maria, A.;De Pedis, D.;Del Gaudio, M.;DeMarco, D. A.;Fabbri, L.;Farina, C.;Fischer, A.;Francis, D.;Gabrielli, A.;Gabrielli, A.;Glasman, C.;Iacobucci, G.;Iodice, M.;Jackson, B.;La Rotonda, L.;Le, B.;Li, C.;Li, Q.;Li, S.;Liu, J.;Liu, L.;Liu, M.;Liu, Y.;Lu, N.;Madaffari, D.;Mancini, G.;Martinez, M.;Mastroberardino, A.;Melo, M.;Meoni, E.;Merola, L.;Perini, L.;Petrucci, F.;Ragusa, F.;Rinaldi, L.;Scarfone, V.;Schioppa, M.;