Measurement of electroweak production of two jets in association with a Z boson in proton-proton collisions at $\sqrt{s}=8\,\text {TeV}$

The purely electroweak (EW) cross section for the production of two jets in association with a Z boson, in proton–proton collisions at $\sqrt{s}=8\,\text {TeV}$ , is measured using data recorded by the CMS experiment at the CERN LHC, corresponding to an integrated luminosity of 19.7 $\,\text {fb}^\text {-1}$ . The electroweak cross section for the $\ell \ell \mathrm {jj}$ final state (with $\ell = \mathrm {e}$ or $\mu$ and j representing the quarks produced in the hard interaction) in the kinematic region defined by $M_{\ell \ell } >50$ $\,\text {GeV}$ , $M_\mathrm {jj} >120$ $\,\text {GeV}$ , transverse momentum $p_\mathrm {T j}> 25$ $\,\text {GeV}$ , and pseudorapidity $|\eta _\mathrm {j} |< 5$ , is found to be $\sigma _\mathrm {EW}(\ell \ell \mathrm {jj})=174 \pm 15\,\text {(stat)}\pm 40\,\text {(syst)}\text {\,fb}$ , in agreement with the standard model prediction. The associated jet activity of the selected events is studied, in particular in a signal-enriched region of phase space, and the measurements are found to be in agreement with QCD predictions.