ZZ Production and Limits on Anomalous Triple Gauge Couplings with the ATLAS experiment at the LHC

This thesis presents an analysis of ZZ production in proton-proton collisions at √s = 7 TeV using data collected in 2011, corresponding to 4.6 fb−1 of integrated luminosity, recorded by the ATLAS experiment at the Large Hadron Collider. Events in the ZZ → l+l − ν ν ( = e, μ) channel are selected and the pp → ZZ →l+l-ν ν cross-section is measured in a restricted phase space. A total ZZ production cross-section is measured for a phase space where both Z bosons are produced in the mass range 66 to 116 GeV, σ(pp → ZZ) = 5.5+/-1.3 (stat.) +1.2_{-1.5} (syst.) +0.4_{-0.3} (lumi.) pb, consistent with the next-to-leading order standard model prediction of 5.81+0.22_{-0.18} pb. Observed event yields in three bins of the transverse momentum of the visible Z are used to set 95% CLs limits on anomalous neutral triple gauge boson coupling parameters f^{V}i0 (V=γ,Z) (i = 4, 5), which parameterize an effective VZZ vertex with both Z bosons on-shell, and which vanish in the standard model. The limits obtained are |f^{γ}40 | < 0.025, |f^{Z}40 | < 0.021, |f^{γ}50 | < 0.026, and |f^{Z}50 | < 0.022, assuming a form factor parameter of Λ = 3 TeV. Additionally, this thesis includes studies of predicted trigger rates of the ATLAS Level-1 calorimeter trigger at luminosities of up to 5 × 10^34 cm−2 s−1 at √s = 14 TeV. The effect of increased granularity calorimeter information on the performance of the Level-1 hadronic τ triggers is investigated. It is found that background rejections of 35-40% would be possible with a 95% signal efficiency, relative to the existing trigger algorithm.