The upgraded ATLAS detector for the search of new physics with diboson final states

Δέσποινα Δ. Σαμψωνίδου
In this dissertation, a study of WZ inclusive production as well as WZ production via the Vector Boson Scattering (VBS) process from proton-proton collisions at the Large Hadron Collider (LHC) at CERN is presented. The data analyzed in this study were recorded by the ATLAS experiment and correspond to integrated luminosity of 36.1 fb−1 at a centre-of-mass energy of 13 TeV. We select events consistent with fully leptonic WZ decays to electrons and muons only. In this doctoral thesis, the muon
more » ... iciency in the forward region of the ATLAS detector is presented. "Scale factors" were provided to scale the muon efficiency in the Monte Carlo simulations, to match the muon efficiency observed in data. These results were used in all ATLAS Run-II analyses using muons.The WZ events are required to have three isolated leptons and missing transverse energy. The major background to the signal are events from ZZ, Z+jets and ttbar production. The background from ZZ is estimated from Monte Carlo simulations, and the Z+jets and ttbar background is estimated from data. The measured inclusive cross section in the detector fiducial region for a single leptonic decay mode was measured to be: σfid = 63.7 ± 1.0(stat.) ± 2.3(syst.) ± 1.4(lumi.)fb.The WZ VBS events are selected from the WZ events, by requiring two additional energetic (pT > 40GeV ) jets with opposite pseudorapidity and dijet invariantmass above 500 GeV. The major background to the WZ VBS are the WZjj areevents originating from QCD processes, the ttV , where V is a W or a Z, and the ZZjj. These are estimated from Monte Carlo simulations which were scaled to match the data in appropriate control regions. The measured cross section in the detector fiducial region for a single leptonic decay mode was measured: σEW(W±Zjj→lνlljj)=0.57 ±0.14 −0.13(stat.) ±0.05 (sys.)0.04 (th.)fb. In addition, the potential effect of New Physics on the WZ inclusive and VBS process through Effective Field theory operators (of Dimension-6 and Dimension- 8) is studied evaluating the potential ef [...]
doi:10.26262/ fatcat:b77zk72ewfhofjmgbmbpv47zg4