Measurement of the cross-section for electroweak production of dijets in association with a $Z$ boson in $pp$ collisions at $\sqrt{s}=13$ TeV with the ATLAS detector

TL;DR

This paper measures the electroweak production cross-section of Z boson-associated dijets at 13 TeV using ATLAS data, confirming Standard Model predictions and distinguishing electroweak from Drell-Yan processes.

Contribution

It provides the first measurement of the electroweak Z+2 jets cross-section in proton-proton collisions at 13 TeV with a data-driven separation method.

Findings

Electroweak Zjj cross-section measured as 119±20 pb for M_jj>250 GeV.

Measured cross-section for M_jj>1 TeV is 34.2±5.8 pb.

Standard Model predictions agree with the measured values.

Abstract

The cross-section for the production of two jets in association with a leptonically decaying Z boson ($Zjj$) is measured in proton-proton collisions at a centre-of-mass energy of 13 TeV, using data recorded with the ATLAS detector at the Large Hadron Collider, corresponding to an integrated luminosity of 3.2 fb$^{-1}$. The electroweak $Zjj$ cross-section is extracted in a fiducial region chosen to enhance the electroweak contribution relative to the dominant Drell-Yan $Zjj$ process, which is constrained using a data-driven approach. The measured fiducial electroweak cross-section is $\sigma^{Zjj}_{EW}= 119\pm 16 (\mathrm{stat.}) \pm 20 (\mathrm{syst.})\pm 2 (\mathrm{lumi.})$ for dijet invariant mass greater than 250 GeV, and $34.2\pm 5.8 (\mathrm{stat.})\pm 5.5 (\mathrm{syst.})\pm 0.7 (\mathrm{lumi.})$ for dijet invariant mass greater than 1 TeV. Standard Model predictions are in agreement with the measurements. The inclusive $Zjj$ cross-section is also measured in six different fiducial regions with varying contributions from electroweak and Drell-Yan $Zjj$ production.