1. LHC@ATLAS Status and Recent Results Ljiljana Simic Institute of Physics, Belgrade Gravity: New ideas for unsolved problems Divcibare, 2011 In honour of 67 th birthday of Milutin Blagojevic 1

2. 2 LHC From the civil engineering, to the manufacturing of the various magnet types, each building block of this extraordinary machine required ambitious leaps in innovation… …There were many challenges - scientific, technological, managerial that had to be met during the various phases of R&D, industrialization, construction, installation and commissioning. L. Evans (LHC Project Leader, 1994-2008). “Thanks to the superb performance of the LHC, we have recorded a huge amount of new data over the last month. This has allowed us to make great strides in our understanding of the Standard Model and in the search for the Higgs boson and new physics.” ATLAS spokesperson Fabiola Gianotti, Geneva, 26 August 2011 “It’s great that the LHC’s fantastic performance this year has brought us this close to a region of possible discovery. Whatever the final verdict on Higgs, we’re now living in very exciting times for all involved in the quest for new physics.” CMS spokesperson Guido Tonelli, Geneva, 26 August 2011

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12. 30 March, 2010, First 7 TeV collisions First 7 TeV collisions on March 30 th

13. What do experiments want? High energy High luminosity “ N = bunch population n b = number of bunches f rev = revolution frequency σ x,y = colliding beam sizes F = geometric factor Depends on machine parameters: charge per bunch (N), num. of bunches (n b ) and transverse beam sizes (σ) Determined by the maximum field of bending dipoles, B B = bending field ρ = bending radius p = momentum e = charge

14. LHC design parameters Excellent LHC performance: - maximum #bunches - 1331, peak stable luminosity delivered: 2.37x10 33 cm -2 s -1 - maximum luminosity delivered: - in one day - 97.4 pb -1, in 7 days - 499.45 pb -1 (02- 08/08/11) - longest time of stable beam – 26 h - maximum peak events number per bunch crossing: 14.01

15. 15 Total Integrated Luminosity in 2011

16. Pile-up challenge in 2011 Event with 11 vertices and 1 Z -Detailed ATLAS performance studies in presence of high pile-up - Understanding impact with data & simulation

17. 17 ATLAS: running smoothly with > 95% data taking efficiency, 2.55 fb -1 of 2011 data recorded by 8 September!

18. ATLAS Operation Status SubdetectorSubdetector #Channels Approx. Operational Fraction#ChannelsApprox. Operational Fraction Pixels 80 M 96.9% SCT Silicon Strips 6.3 M 99.1% TRT Transition Radiation Tracker 350 k 97.5% LAr EM Calorimeter 170 k 99.5% Tile calorimeter 9800 97.9% Hadronic endcap LAr calorimeter 5600 99.6% Forward LAr calorimeter 3500 99.8% LVL1 Calo trigger 7160 99.9% LVL1 Muon RPC trigger 370 k 99.5% LVL1 Muon TGC trigger 320 k 100% MDT Muon Drift Tubes 350 k 99.8% CSC Cathode Strip Chambers 31 k 98.5% RPC Barrel Muon Chambers 370 k 97.0% TGC Endcap Muon Chambers 320 k 98.4% Relative fraction of good quality data delivered by the various ATLAS Subsystemsbetween 90 and 100%.

19. Performance for physics 19 P T jet (GeV) m ee (GeV) m µµ (GeV)

20. ATLAS submitted/published 63 papers on collision data (15 in August) Minimumbias, Jets, W,Z, Prompt Photons, Dibosons, Top quark, B physics, Higgs Supersymmetry, Exotics, Heavy Ions

21. Soft-QCD in a new high energy and high multiplicity frontier 21 arXiv: 1003.3124 ; arXiv:1012.5104 Phys. Lett. B 688,1,21; New J. Phys. 13,053033 (2011) We have to use the soft QCD distributions to test the phenomenological models and “tune” the Monte-Carlo event generators to give the best description of the data Fully inclusive-inelastic distributions in data with no model dependent corrections are compared to different MC models, and significant differences were observed. Pre-LHC models seen not to agree with most of the “soft”-QCD distributions

22. Soft-QCD 22 arXiv: 1104.0326 Acc. by Nature Comm. All the pre-LHC MC tunes considered show lower activity than the data in the transverse region arXiv:1012.0791v2 arXiv:1103.1816v2 Underlying Event Coming soon: interesting UE results with leading jet, in Z-boson events Full Inelastic Cross-Section An inelastic cross-section of 60.3 ±2.1 mbis measured for ξ> 5 x 10 -6. Compares to 64.7 mb from Pythia (1.2σ) and 73.5 mb from Phojet (2.5σ). Hot topic at hadron colliders since the 1960’s

23. Jets: Impresiv agreement between data and theory 23 Inclusive jet cross sectionDijet cross sectionMultijet cross section Jet production is the dominant high-pT process in p-p collisions. Provides a stringent test of QCD at the TeV scale. Inclusive and dijet cross sections are presented covering a phase space among the widest currently accessed in collider physics. Measurements in which specific dijet and multijet configurations are selected to enhance sensitivity to higher order effects, allowing the study of QCD radiation at large rapidity intervals. Measurements of heavy flavours in jets, the internal structure of jets, and of single-jet mass which carry information about soft physics and the QCD cascade..

24. ATLAS W, Z and Top Cross Sections Summary 24 All measurements agree with SM expectation (so far) Probing cross sections of ~10 pb ATLAS-CONF-2011-010 ATLAS-CONF-2011-041 ATLAS-CONF-2011-042 ATLAS-CONF-2011-060 ATLAS-CONF-2011-099 ATLAS-CONF-2011-107 ATLAS-CONF-2011-110

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26. Top Quark Pair Cross Section Summary 26 ATLAS-CONF-2011-100, ATLAS-CONF-2011-101, ATLAS-CONF-2011-106, ATLAS-CONF-2011-108, Dependence of σtt on √s from theoretical predictions based on a top mass of 172.5 GeV together with the dilepton, single lepton, and combined measurements from ATLAS ATLAS (up to 0.7 fb -1 ) Measurements agree with QCD predictions (although a little higher) The top quark is the heaviest known elementary particle, and could play a special role in the Standard Model. Its coupling to the Higgs boson is large, and it could also play a role in electroweak symmetry breaking and the generation of particle masses in alternatives to the Higgs mechanism.

27. 27 SM Higgs Production at the LHC

28. 28 SM Higgs Decay Modes

29. Higgs search at ATLAS 29 The combined upper limit on the Standard Model Higgs boson production cross section divided by the SM expectation as a function of Higgs mass (solid line), ATLAS-CONF-2011-135, 22/08/2011. A wide range of Higgs search channels cover Higgs masses from 110 to 600 GeV The Higgs boson mass ranges from 146 to 232 GeV 256 to 282 GeV 296 to 466 GeV are excluded at 95% CL. An excess of events is observed in the low mass range. Its significance is at most approximately 2  above expected SM background. Channels included: H , WH  l  bb ZH  llbb H  WW  l  l  H  ZZ  4l H  ZZ  ll  H  ZZ  llqq H  ZZ  llbb H  WW  l  l 

30. 30 Where we are now!

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32. Searches for Physics Beyond SM 32 Search for W’ with 1.04 fb -1 of 2011 data exclude m(W’)<2.15 TeV for SM couplings combining eν and μν decay modes arXiv: 1108.1316 Dijet resonance search with 0.81 fb - 1 of 2011 data excludes excited quarks with M(q*)<2.91 TeV and axigluons with M(A)<3.21 TeV and color octet scalar resonances with m(s8)<1.91 TeV. ATLAS-CONF-2011- 095 Invariant mass distribution of jet pairs produced in association with a leptonically decaying W boson using 1.02 fb-1 of 2011 data. No excess over SM data. ATLAS-CONF-2011-097 No sign of disagreement with SM expectation Search for SUSY in final states with one isolated e, µ, jets and E T miss with 165 pb -1

33. Conclusions The LHC and ATLAS are working very well An abundance of important measurements now available at 7TeV Now pushing deep into unexplored regions of phase space with both simple and complex search topologies Major increase in sensitivity with 1 - 2.3 fb -1 of 2011 data As yet no conclusive evidence of Higgs production ATLAS excludes at 95% CL production of Standard Model Higgs boson over 146-252 GeV, 256-282 GeV and 296-466 GeV 33