Observation and measurements of the production of prompt and non-prompt $J/ψ$ mesons in association with a $Z$ boson in $pp$ collisions at $\sqrt{s}= 8$ TeV with the ATLAS detector

ATLAS Collaboration

Published 2014-12-19Version 1

The production of a $Z$ boson in association with a $J/\psi$ 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 $20.3$ fb$^{-1}$ of data collected with the ATLAS experiment at the LHC, in $pp$ collisions at $\sqrt{s}=8$ TeV, the first measurement of associated $Z + J/\psi$ production is presented for both prompt and non-prompt $J/\psi$ production, with both signatures having a significance in excess of $5\sigma$. The inclusive production cross-sections for $Z$ boson production (in $\mu^+\mu^-$ or $e^+e^-$ decay modes) in association with prompt and non-prompt $J/\psi(\to\mu^+\mu^-)$ are measured relative to the inclusive production rate of $Z$ bosons in the same fiducial volume to be $(88\pm 16\pm 6) \times 10^{-8}$ and $(157\pm 22\pm 10) \times 10^{-8}$ respectively. Normalised differential production cross-sections are also determined as a function of the $J/\psi$ 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 at $68\ (95)$% confidence level is placed on the effective cross-section regulating double parton interactions.