The ATLAS Experiment at the LHC Exploring the high-Energy Frontier of Particle Physics University of Tokyo, 25th January 2007 (P. Jenni, CERN) University of Tokyo, 25-Jan-2007, P. Jenni (CERN)

Search for the Higgs boson ATLAS H  ZZ(*)  4 Simulation of a H   ee event in ATLAS University of Tokyo, 25-Jan-2007, P. Jenni (CERN)

SM Higgs in ATLAS and CMS Events / 0.5 GeV ATLAS + CMS preliminary 1 10 10-1 Needed Ldt (fb-1) per experiment mH (GeV)  1 fb-1 for 98% C.L. exclusion  5 fb-1 for 5 discovery over full allowed mass range --- 98% C.L. exclusion here discovery easier with gold-plated H  ZZ  4l  by end 2008 ? University of Tokyo, 25-Jan-2007, P. Jenni (CERN)

Light Higgs: more difficult case…. K-factors  (NLO)/(LO)  2 for H  NOT included (conservative) mH ~ 115 GeV 10 fb-1 : S/B  4 ATLAS 3 (complementary) channels with similar (small) significance: H   b ttHttbb  blbjjbb H  qqH  qq S=130, B=4300, S/B=2 S=15, B=45, S/B=2.2 S=10, B=10, S/B=2.7 different production and decay modes different backgrounds different detector/performance requirements: -- ECAL crucial for H   (in particular response uniformity) : /m ~ 1% needed -- b-tagging crucial for ttH : 4 b-tagged jets needed to reduce combinatorics -- efficient jet reconstruction over || < 5 crucial for qqH  qq : forward jet tag and central jet veto needed against background All three channels require very good understanding of detector performance and background control to 1-10%  convincing evidence likely to come later than 2008 … Note: WH lbb (dominant at the Tevatron) provides less sensitivity than ttH at LHC University of Tokyo, 25-Jan-2007, P. Jenni (CERN)

Conclusions The LHC construction is on track for first collisions end of 2007, and for starting operation at design energy in 2008 Many important milestones have been passed in the construction, pre-assembly, integration and installation of the ATLAS detector Very major software, computing and physics preparation activities are underway as well, using the Worldwide LHC Computing Grid (WLCG) for distributed computing resources The LHC at CERN and ATLAS will open a new era of particle physics, exploring for the first time directly the TeV mass scale  The coming years will certainly be very exciting! (Informal news on ATLAS is available in the ATLAS eNews letter at http://aenews.cern.ch/) University of Tokyo, 25-Jan-2007, P. Jenni (CERN)