Abstract
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.
Highlights
The production of a Z boson in association with two jets in proton–proton collisions is dominated by a mixture of electroweak (EW) and strong processes of order αE2WαS2
DY events are generated with MadGraph using a leading order (LO) matrix element (ME) calculation that includes up to four partons generated from quantum chromodynamics (QCD) interactions
DY Zjj prediction—For the modelling of the DY Zjj background from simulation, as we indicated previously, we consider the full difference between the Born-level MadGraph prediction and the next-to-leading order (NLO) prediction based on mcfm as a systematic uncertainty
Summary
The production of a Z boson in association with two jets in proton–proton (pp) collisions is dominated by a mixture of electroweak (EW) and strong processes of order αE2WαS2. Electroweak jj production contributing to the same final state is expected at order αE4W, resulting in a comparatively small cross section [1]. This process is predicted to have a distinctive signature of two jets of very high energy and large jj invariant mass, Mjj, separated by a large rapidity interval that can be occupied by the two charged leptons and where extra gluon emission is suppressed [2,3]. The analysis of the 8 TeV data, offers the opportunity of reducing the uncertainties of the 7 TeV measurements, given the larger integrated luminosity, and to add robustness to the results with the new data-based method
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