Study of ZW ^± ,and ZZ Production Using ATLAS Full Simulation Data
 
The study of the diboson final states has been our focus during the past year. The diboson production involves the trilinear gauge boson couplings (TGCs) which is a direct consequence of the non-Abelian SU(2) ´ U(1) gauge structure of the standard model (SM). We plan to use the early LHC data to measure the diboson production cross-sections and the TGCs to test the SM, as well as search for new physics beyond the SM. Further more, it is crucial to understand the diboson event rates and event topologies since they are the background for many important new physics searches at the LHC. For example, WW and ZZ are the background sources for Higgs searches via H ® ZZ, ZZ^*, WW, WW^* decay channels; the WZ final state would be the dominant background contribution for the search for Super-Symmetry particles; and WW would be the background source of the search for the graviton in extra-dimension models and the new gauge boson Z’.
We have, for the first time at ATLAS, studied the ZW ^± ,and ZZ production in pp collision at 14 TeV center-of-mass energy using full simulation data-sets based on Geant-4 with the ATLAS initial detector layout. About 0.1 million signal events are generated by MC@NLO (v.2.3) and the events are selected according to the electrons and muons decayed from Z or W. About 14 million, the largest and most completed SM background events at ATLAS, are generated at Michigan with Pythia to study the backgrounds sources of diboson production. For an integrated luminosity of 1 fb^-1 data, we expect to observe 76 ZW signal events and 6 background events in the eee n , ee mn , e mmn and mmmn channels; 284 WW signal and 59 background events in the ev mn channel; and, 13 ZZ signal events in the 4 lepton final states (eeee, mmmm and ee mm ) with negligible background events. Our studies show that even with 100 pb^-1 ATLAS data, we should be able to well establish the WW and the ZW diboson signals, and thus measure the production cross-section and the TGCs.
Our results have been submitted as ATLAS physics analysis note (ATL-COM-PHYS-2006-033 ) , and presented at ATLAS Annual Meeting held in Rome in 2005, and the North American Higgs and Standard Model Workshop held at Argonne National Laboratory in April 2006.
We are now working on generating and validating ATLAS Data Challenge III data for the diboson production using new event generator, MC@NLO (v.3.1) . Our plan is to further optimize the analysis event selection, apply new analysis techniques for the signal selection and background rejection such as boosted decision trees and artificial neural networks, and study the systematic uncertainties. We are also planning to develop the programs necessary to extract the TGCs from the diboson event analysis. Our study has been listed as one of the early LHC physics topics for publication in ATLAS physics group.