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

Abstract

The production of two prompt J/ψ mesons, each with transverse momenta p T > 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 ATLASdetector at the LHC. The differential cross-section, assuming unpolarised J/ψ production,is measured as a function of the transverse momentum of the lower-p T J/ψ meson, di-J/ψp T and mass, the difference in rapidity between the two J/ψ mesons, and the azimuthalangle between the two J/ψ mesons. The fraction of prompt pair events due to double partonscattering is determined by studying kinematic correlations between the two J/ψ mesons.The total and double parton scattering cross-sections are compared with predictions. Theeffective cross-section of double parton scattering is measured to be σ eff = 6.3 ± 1.6(stat) ±1.0(syst) mb.