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

A key observable for understanding the quarkonium production mechanism is the associated production of a vector boson with heavy quarkonia. ATLAS Collaboration in LHC observed the associated production of prompt and non-prompt $J/\psi$ mesons with $Z$ boson with $5\sigma$ and $9\sigma$ signifance respectively. In this poster the measurement of the production rate of $Z+J/\psi$ over inclusive $Z$ is discussed. Additionaly, contributions from single and double parton interactions are evaluated and the results are compared to latest theoretical calculations in the colour singlet and colour octet formalisms. Finally, a lower limit in the double parton scattering effective cross section is extracted.