Searches for Continuum and Resonant Production of Z Boson Pairs Using the ATLAS Detector

We present a search for Z boson pair production in a 3 lepton channel using the ATLAS detector at sqrt(s) = 14 TeV. The search was motivated by the inefficiencies in electron reconstruction in the 4 lepton channel. Although the 3 lepton channel has a higher acceptance, it suffers from a high background which consists of Zbb, Zb, WZ, and tt. We used different clustering algorithms with a higher pseudorapidity coverage to partially identify the missing electron. The analysis was performed using Monte Carlo samples generated by different event generators, and the ATLAS detector was simulated by the GEANT4 software. We estimate a gain of 38% of the acceptance of ZZ events with respect to an explicit fully reconstructed 4 lepton final state ZZ to 4l. In terms of the significance defined as S /sqrt(S+ B), we obtain an increase from 3.6 to 4.1. We also performed a Higgs search in the mass range of mH>180 GeV in the channel H-->ZZ-->4l, where the two Z's are on-shell. This allowed us to use the same event selection criteria used in the case of the ZZ analysis. For a Higgs boson mass of 200 GeV, the luminosity required to achieve 5 sigma decreases from 6.8 fb-1 with a fully reconstructed 4 lepton final state to 5.4 fb-1 when the 3 lepton analysis is combined with the 4 lepton channel. We present also how one fares for a lower mass study.