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)} mb.
Highlights
J/ψ production, is measured as a function of the transverse momentum of the lower- pT J/ψ meson, di-J/ψ pT and mass, the difference in rapidity between the two J/ψ mesons, and the azimuthal angle between the two J/ψ mesons
The PP di-J/ψ and DPS differential cross-sections in the central and forward rapidity regions are measured for the sub-leading J/ψ pT, the di-J/ψ pT, and the di-J/ψ invariant mass corrected for the muon kinematic acceptance
The fraction of DPS events is calculated for each distribution, and the distributions are compared to the LO DPS and NLO* subtracted and corrected DPS (SPS)+DPS predictions
Summary
It is expected that DPS plays a larger role at high energies and could be increasingly important for ccccproduction [21,22]. Due to the low production rate of prompt J/ψ meson pairs, this process has not been studied in as much detail as other DPS processes and can provide a good test of the process dependence of the effective cross-section. The differential cross-section over the full J/ψ rapidity region defined by the muon selection criteria is measured for these variables along with the difference in rapidity and the azimuthal angle between the two. 2011, the CMS experiment measured the cross-section of the pair production of prompt J/ψ mesons extrapolated to a muon pT of zero assuming unpolarised J/ψ mesons [44]. The D0 experiment using measured the fidu√cial data collected at s prompt J/ψ pair cross-section = 1.96 TeV [29]. The present region using measurement data collected of PP di-J/ψ production uses a different kinematic range and a larger data set.
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