The ATLAS Experiment at the CERN LHC

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The CERN Large Hadron Collider (LHC) has the highest direct energy reach of any particle physics facility, and Canada's central role in the ATLAS collaboration at the LHC will keep us at the forefront of international particle physics. ATLAS and the LHC conducted our first major operational period, called Run 1, in 2011 and 2012, with proton-proton collision centre-of-mass energies of 7-8 TeV. With those data, ATLAS, together with the CMS collaboration, discovered the Higgs boson whose existence was predicted in 1964 and intensely sought over the intervening half century. The Higgs discovery was covered widely by International and Canadian media and led directly to the award of the 2013 Nobel prize in physics to Peter Higgs and Francois Englert. Studies of the properties of the newly observed Higgs particle have so far shown it to be consistent with the Standard Model Higgs, but the limited number of Higgs particles observed at the LHC restrict the sensitivity of the results. Canadians played leading roles in several of the analyses used to discover the Higgs boson and to measure its properties, including the current coordination of the ATLAS Higgs working group. The Higgs boson discovery was a remarkable achievement, but only scratches the surface of the potential physics reach of ATLAS and the LHC, which were designed from the outset to probe for signatures of new physics at the TeV scale that could "stabilize" the vacuum and address deficiencies of the Standard Model. Achieving the full potential of ATLAS requires more data at higher energies. The three-year running period covered by this project grant request, Run 2 from spring 2015 to spring 2018, will see the higher luminosities and energies required to push our understanding of matter and energy beyond the Standard Model. This is the most critical running period for pushing our knowledge beyond the Standard Model. Support of Canadian ATLAS operations over the coming three years will ensure that we reap the benefits from our significant investment in ATLAS and the LHC, extracting maximal and diverse physics output while training the next generation of Canadian particle physicists. ATLAS and the LHC are designed to directly address some of the most compelling questions in science. Even with the Higgs observed, the Standard Model is problematic if no new physics with electroweak couplings is present below about 1 TeV, and ATLAS and the LHC will definitively explore this region in Run-2 and discover the physics beyond the Standard Model that seems to lurk just within our reach. With ATLAS and the LHC engaged in collision operations, the ATLAS-Canada request will be focused on detector and computing operations and physics analysis. The request includes postdoctoral fellow and student support, travel to CERN for expert activities and physics meetings, CERN subsistence for CERN-based personnel, and travel for physics meetings and conferences.