CERN-LHC. Measurements of the cross-section of the electroweak production in Zy final state in association with two jets, using two decay channels Z -> l+ l- and Z -> nu nu~ (with l=e,mu and nu=e/mu/tau neutrinos and nu~=e/mu/tau anti-neutrinos and y=photons) in proton-proton collision data corresponding to an integrated luminosity of 20.2 fb-1 at a centre of-mass energy of 8 TeV with the ATLAS detector at the Large Hadron Collider. Limits are also sets on WWZy/ZZZy/ZyZy/yyZy anomalous quartic gauge couplings.
The charged-leptonic channel Zyjj electroweak process cross sections are measured in two regions, one of which is constructed with maximized sensitivity to Zyjj electroweak process (SR) and the other region is defined as the Zyjj QCD process control region (CR). A further optimized region with higher Et photon cut applied is used to probe the anomalous quartic couplings (aQGC). The neutrino channel is probed in a region used to further improve the sensitivity to aQGC and combined with charged leptonic channel. The detailed definitions are summarized as follows.
The charged-leptonic channel (Z -> l+ l- ) is defined as (the exact definition is given in table 5 of the preprint):
- 2 Same Flavor Opposite Sign (SFOS) leptons (electrons or muons) with pT(Lepton)>25 GeV and |eta(Lepton)|<=2.5
- 1 isolated photon with ET(Photon)>15 GeV and |eta(Photon)|<=2.37
- 2 jets with pT(Jet)>30 GeV and |eta(Jet)|<4.5
- |m(LeptonLepton) + m(LeptonLeptonPhoton)| > 182 GeV, |m(LeptonLepton)|>40 GeV
- DeltaR(Lepton, Photon)>0.4, DeltaR(Jet, Photon)>0.4, DeltaR(Jet, Lepton)>0.3
- SR is defined with |m(JetJet)|>500 GeV
- CR is defined with 500 GeV>|m(JetJet)|>150 GeV
- aQGC search region is defined on top of SR with ET(Photon)>250 GeV
- Requirement of Photon isolation (particle level only): ET(isolation)/ET(Photon) < 0.5. The photon isolation energy is taken as the energy of the jet matching the photon (DeltaR(Jet, Photon)<0.3), with the photon energy subtracted.
The neutrino channel (Z -> nu nu~) is defined as (the exact definition is given in table 8 of the preprint):
- two-neutrino-system pT>100 GeV
- 1 isolated photon with ET(Photon)>150 GeV and |eta(Photon)|<=2.37
- 2 jets with pT(Jet)>30 GeV and |eta(Jet)|<4.5
- |m(LeptonLepton) + m(LeptonLeptonPhoton)| > 182 GeV, |m(LeptonLepton)|>40 GeV
- DeltaR(Jet, Photon)>0.4
- |m(JetJet)|>600 GeV
- Rapidity gap between two jets greater than 2.5
- photon centrality less than 0.3 and event pT balance less than 0.1 (variable definitions can be found in equation 1 and 2 of the preprint)
- DeltaR(ET(NeutrinoNeutrino), JetJetPhoton)>3*PI/4., DeltaR(ET(NeutrinoNeutrino), JetJetPhoton)>PI/2., DeltaR(ET(NeutrinoNeutrino), Jet)>1.
- Requirement of Photon isolation (particle level only): ET(isolation)/ET(Photon) < 0.5. The photon isolation energy is taken as the energy of the jet matching the photon (DeltaR(Jet, Photon)<0.3), with the photon energy subtracted.
