Experimental study of particle physics in TeV region at LHC

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Standard model explains the origin of particle masses with the Higgs mechanism. Self interaction of scalar particles result in a spontaneous symmetry breaking of the vacuum. One scalar particle, called Higgs particle, is a physically observable particle. Its mass is expected to be less than approximately 1 TeV.Supersymmetric particles are also expected to be in this energy region. Large Hadron Collider (LHC) project at CERN was officially approved in December 1994, and is scheduled to be operational in 2005. LHC is a proton-proton collider with the beam energy of 7 TeV,approximately one order of magnitude higher than the present highest machine energy. ATLAS experiment is a general purpose detector to study the 1 TeV energy region using this machine.We have been doing research and development for the ATLAs detector in collaboration with physicists from 33 countries. We have been contributing to the following five items : (1) Muon detector and trigger system, (2) Silicon detector, (3) Superconducting solenoid, (4) High-speed data acquisition sytem, and (5) Software for physics analysis. As for the muon detector and trigger system, we submitted a detailed technical design report (TDR). We are totally responsible for the construction of the superconducting solenoid with 2 tesla of a mgnetic field. A detailed TDR was submitted, and the solenoid is now under construction. As for the trigger system and the high-speed data acquisition system, we have done detailed design, and are preparing for a TDR.As for the software, we developed software tools based on object oriented technology. We especially concentrated on "GEANT4", a detailed detector simulation package. Throughout the research and developments in the ATLAS collaboration, close contact and dense discussions with collaborators are essential. It was only possible to make fruitful research with using the grant-in-aid.