Measurement of the prompt \(J/\psi\) pair production cross-section in pp collisions at \(\sqrt{s} = 8\) TeV with the ATLAS detector

Abstract

The 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 \(\sigma_{\mathrm{eff}} = 6.3 \pm 1.6 \mathrm{(stat)} \pm 1.0 \mathrm{(syst)} \pm 0.1 \mathrm{(BF)} \pm 0.1 \mathrm{(lumi)}\) mb.