UC Santa Cruz

The production of a Z$$Z$$ boson in association with a J/ψ$$J/\psi $$ meson in proton–proton collisions probes the production mechanisms of quarkonium and heavy flavour in association with vector bosons, and allows studies of multiple parton scattering. Using 20.3fb-1$$20.3\,\text {fb}^{-1}$$ of data collected with the ATLAS experiment at the LHC in pp$$pp$$ collisions at s=8TeV$$\sqrt{s}=8\,\text {TeV}$$, the first measurement of associated Z+J/ψ$$Z\, +\, J/\psi $$ production is presented for both prompt and non-prompt J/ψ$$J/\psi $$ production, with both signatures having a significance in excess of 5σ$$5\sigma $$. The inclusive production cross-sections for Z$$Z$$ boson production (analysed in μ+μ-$$\mu ^+\mu ^-$$ or e+e-$$e^+e^-$$ decay modes) in association with prompt and non-prompt J/ψ(→μ+μ-)$$J/\psi (\rightarrow \mu ^+\mu ^-)$$ are measured relative to the inclusive production rate of Z$$Z$$ bosons in the same fiducial volume to be (36.8±6.7±2.5)×10-7$$(36.8\pm 6.7\pm 2.5)\, \times \, 10^{-7}$$ and (65.8±9.2±4.2)×10-7$$(65.8\pm 9.2\pm 4.2)\, \times \, 10^{-7}$$ respectively. Normalised differential production cross-section ratios are also determined as a function of the Jψ$$\text {J}\uppsi $$ transverse momentum. The fraction of signal events arising from single and double parton scattering is estimated, and a lower limit of 5.3(3.7)mb$$5.3\ (3.7)\,\text {mb}$$ at 68(95)%$$68\ (95) \%$$ confidence level is placed on the effective cross-section regulating double parton interactions.