Status of the ATLAS Experiment Epiphany 2011 Matthias Schott (CERN) - PowerPoint PPT Presentation

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Status of the ATLAS Experiment Epiphany 2011 Matthias Schott (CERN)

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  1. Status of the ATLAS Experiment Epiphany 2011 Matthias Schott (CERN) On behalf of the ATLAS Collaboration • Content • ATLAS Detector and Data Taking • Detector Performance • Highlights of the 2010 Physics Results • Prospects and Conclusion

  2. Content • ATLAS Detector and Data Taking • Detector Performance • Highlights of the 2010 Physics Results • Prospects and Conclusion • Summary • Overview of the ATLAS Collaboration and the ATLAS Detector • Brief discussion on the data taking in 2010 and triggering • Data processing

  3. The most exciting LHC year so far: 2010 March 2010: ATLAS Control Room May 2010: First Z Candidate November 2010: Pb-Pb collision July 2010: First Top Candidate

  4. The ATLAS Collaboration • 3000 scientists • 174 institutes • 38 countries • all continents • More than 1000 PhD students • More than 1.200 working meetings each month • Increased by factor of 3 compared to pre-data period

  5. The ATLAS Detector • Inner Detector • |η|<2.5, solenoid B=2T • Si Pixels, Si strips, TRT • Tracking and vertexing • e/π separation • Resolution: σ/pT~3.8x10-4pT[GeV]⊕0.015 • EM calorimeter • |η|<3.2 • LAr/Pb accordion structure e/γ trigger, id + measurement • E-resolution: σ/E ~ 10%/√E • HAD calorimeter • |η|<3.2 (Forward Calo. |η|<4.8) • Scint./Fe tiles in the central, W(Cu)/LAr in fwd region • Trigger, jets + missing Et • E-resolution: σ/E ~ 50%/√E ⊕ 0.03 • Muon Spectrometer • |η|<2.7 • Toroid B-Field • Muon Momentum resolution < 10% up to ~ 1 TeV

  6. Data Taking (1/2) • 48.1pb-1 delivered integrated luminosity • Many thanks to a fantastic LHC team • Luminosity detectors calibrated with van der Meer scans • Luminosity known today to 11% (error dominated by knowledge of beam currents) • Will go down significantly after analysis of last van der Meer scan (done on 1st Oct 2010) • ALFA detector in place for 2011 • elastic scattering in Coulomb-Nuclear interference region • Overall ATLAS Data-taking efficiency: 93.6%

  7. Data Taking (2/2) • For all systems > 97% of channels are operational • in addition have built-in redundancy in most systems • Total fraction of good quality data • Constantly >94% • Typical LHC Fill • Few minutes needed for tracking detectors (silicon and muons) to ramp HV when LHC declares stable beams • Short ‘dips’ in recorded rate: recover “on-the-fly” modules which would otherwise give a BUSY blocking further events

  8. Trigger (1/2) • Level-1: • Implemented in hardware • Muon + Calo based • coarse granularity • e/γ, μ, π, τ, jet candidate selection • Define regions of interest (ROIs) • Level-2: • Implemented in software • Seeded by level-1 ROIs, full granularity • Inner Detector – Calo track matching • Event Filter: • Implemented in software • Offline-like algorithms for physics signatures • Refine LV2 decision • Full event building • Collision rate 40MHz • LV1 accepts up to 75kHz • recorded ~300 Hz

  9. Trigger (2/2) • Trigger configuration infrastructure is very flexible • Coping very well with rapidly increasing luminosity by adjusting prescales/menus • ~10 different inclusive streams written out during the run • Challenges • optimize sharing of the bandwidth for physics • Determination of trigger efficiencies in data • Level-1 Muon Trigger efficiency determined with ‘tag-and-probe’ method on J/Psi candidates Combined muon track pT

  10. Data Processing • 10 GB/s peak rate during data and MC processing • Design was 2GB/s • Reprocessing of all MC and Data during LHC data taking • More than 1000 users running analysis jobs on the GRID • Over 1000 different users during past 6 months • Millions of jobs are ran every week at hundreds of sites • Data distribution on the Grid • Constant impressive duty cycle !

  11. Content • ATLAS Detector and Data Taking • Detector Performance • Highlights of the 2010 Physics Results • Prospects and Conclusion • Overview • Discussion of the individual sub-detectors of ATLAS along their corresponding physic objects • Inner Detector • Electrons and Photons • Jets and Missing Energy • Muons

  12. Inner Detector Performance (1/3) • Observed all most classic resonances • Ks, K*, φ, Λ, Ω, Ξ, D, D* and J/Ψ • Momentum scale known to permil level in this range • Is precisely determined via known resonances • Resolution as expected (dominated by multiple scattering) • Good performance of ATLAS tracker and tracking/vertexing algorithm

  13. Inner Detector Performance (2/3) • Today know detector material distribution to better than 10% • Estimation via e.g. • Reconstructed secondary vertices due to hadronic interactions • KS mass • Use γ-ee conversion • Already very good, but can be improved Data MC Cooling Pipe + Cable Bundle

  14. Inner Detector Performance (3/3) • Particles with higher masses (e.g. J/Psi, Z) are used to assess momentum scale and resolution in higher energy regimes • Example: J/Psi mass resolution (see plots) • Momentum scale known to 1% level up to ~100GeV • Offline reconstruction efficiencies determined e.g. via ‘tag and probe’ techniques • Inner Detector reconstruction efficiency for muons above 20GeV confirmed to be better than 99%

  15. Electrons and Photons (1/2) • Main electron selection based on EM calorimeter: • purely electromagnetic shower • shower shapes • pointing track • Refinement via Inner Detector • Conversion detection via inner most pixel layer • e/π0 separation via TRT (upper left plot) • Performance as predicted by Monte Carlo simulations • Impact of ID misalignment on electron identification before reprocessing • Di-Electron Mass Plot based on 5 GeV di-electron trigger • prescaled in later data • produces shoulder at 15 GeV

  16. Electrons and Photons (2/2) • Neutral pions provide handle for measuring EM energy scale and response uniformity • ~2% in η • <0.7% in φ • Good agreement of Z-Boson lineshape • Autumn reprocessing • Energy Scale uncertainty <1% • Aim for electron identification efficiency determination for 2010 data: 1%

  17. Jets and Missing Energy (1/2) • Jet energy computed from calibrated topological clusters • ATLAS Jet Algorithm • anti-KT • jet radius R=0.6, 0.4 • Jet Energy Scale and Resolution • MC studies • many years of detailed test beam studies • JES from collision data • Single hadrons: Ecalo/ptracker (Use isolated tracks, determine calorimeter response for single particles) • di-jets events with η inter-calibration • Determination via Z-Boson and top events • Aim to reach 1%

  18. Jets and Missing Energy (2/2) • Missing transverse energy is key element for many searches and precision measurements • Governed by strong performance of the ATLAS calorimeter • Sensitive to calorimeter performance (noise, coherent noise, dead cells, mis-calibrations, cracks, etc.), and cosmics and beam-related backgrounds • Calibrated ETMiss from minimum-bias events • Plots: ETMiss distribution and resolution as measured in a data sample of 15.2 million selected minimum bias events • No ETMiss tails after calibration • Further calibration channels: Z, W and top decays

  19. Muon Systems (1/2) • Good performance of combined Inner Detector and Muon Spectrometer reconstruction • At low pt, Inner detector is dominating overall muon momentum resolution (~2% resolution, dominated by multiple scattering) • Transition at ~50GeV • Muon Spectrometer Performance can be assessed via • Cosmic muons • Di-muon decays of known particles • Momentum scale known to 1% • Momentum resolution known to rel. 10% • Reconstruction efficiency known to 1-2% • Aim is to reach <1%

  20. Muon Systems (2/2) • Example: First studies of Momentum resolution of MS standalone • cosmics: resolution from splitting muon tracks crossing the detector from top to bottom • muons from collisions: resolution from comparing MS with ID measurement (ID resolution not subtracted, negligible at low p) • Z-Boson resonance appeared wider in data, due to • Alignment, magnetic field uncertainties • Significant improvement after reprocessing after new calibration

  21. Content • ATLAS Detector and Data Taking • Detector Performance • Highlights of the 2010 Physics Results • Prospects and Conclusion • Summary • 15 papers already published based on 2010 collision data • Many more to come in the next weeks • More than 100 approved results for conferences • Only a very small fraction can be shown in an overview talk • Jet Physics, W/Z Boson Production, Exclusion Limits on UED, Top Production and Heavy Ions results • Further reading: https://twiki.cern.ch/twiki/bin/view/AtlasPublic

  22. Jet Physics (1/2) • Inclusive jet cross-section • ~100xTevatron • Restricted to 17 nb-1 (no pile-up contamination); • pT > 60 GeV and |y| < 2.8 • Measured jets corrected to particle level using parton-shower MC • Experimental uncertainties dominated by JES • 9% in pT and y ranges considered • 11% from Luminosity not included • Good data-MC agreement over five orders of magnitude!

  23. Jet Physics (2/2) • Why studying Jet-shapes? • details of the parton-to-jet fragmentation process • internal structure is mainly dictated by the emission of multiple gluons from the primary parton, calculable in pQCD • shape of the jet depends on parton-type that give rise to jets in the final state • sensitive to non-perturbative fragmentation effects • Integrated jet shape Ψ(r) is defined as the average fraction of the jet pT that lies inside a cone of radius r concentric with the jet cone • Excellent agreement with PYTHIA-Perugia2010 tune

  24. W/Z Bosons at ATLAS (1/2) • Why W/Z Bosons production at ATLAS so important? • Fundamental milestones in the “rediscovery”of the Standard Model • Powerful tools to constrain PDFs and test perturbative QCD • Z leptonic decay is gold-plated process to calibrate the detector to the ultimate precision • dominant backgrounds to searches for New Physics • October 2010: First measurement of the W/Z boson production cross-section at 7TeV • Already dominated by Luminosity Uncertainty • Excellent agreement with theoretical predictions • See more details in Pawel’s talk

  25. W/Z Bosons at ATLAS (2/2) • December 2010: First Measurement of W+jets cross-sections at LHC • Highly Important since • Precise test of perturbative QCD • background for top, Higgs and many BSM models (e.g. SUSY) • Select anti-KT jets with radius 0.4, |y|<2.8, full W selection • Alpgen used to produce signal template • Dominating uncertainty: JES • Much more details in Sergei‘s talk

  26. Top Quark (1/2) • arXiv:1012.1792 [hep-ex] • Cross-Section measurement based on 2.9pb-1 • 37 candidate events are observed in the single-lepton topology • 9 events in the dilepton topology • Final Selection for single lepton decay • 1 isolated lepton pT>20 GeV • ETmiss > 20 GeV • ETmiss + mT (W) > 60 GeV • ≥4jets with pT >20GeV • ≥ 1 b-tag jet

  27. Top Quark (2/2) • Dominating Backgrounds • Muon channel: W+jets • Electron channel: QCD, W+jets • Both backgrounds are estimated in a data-driven way • Cross-Section measurement with perfect agreement to theoretical prediction • Most precise measurement at 7TeV • Dominating systematic uncertainties • normalisation of the QCD multi-jet background in the e+jets channel • uncertainties which affect mainly the tt ̄ acceptance: jet energy reconstruction, b-tagging and ISR/FSR

  28. Diphoton Events with Large ETMiss(1/1) • Several new physics models predict much larger γγ + ETMiss rates than SM • Example: Universal Extra Dimension • postulate the existence of additional spatial dimensions • Predict for each SM particle a series of excitations: Kaluza-Klein (KK) tower • Lightest KK particle is γ* which would undergo a cascade decay to γ • Benchmark Model • One single TeV−1-sized UED, with compactification radius R • values of 1/R < 728 GeV are excluded at 95% CL, providing the most sensitive limit on this model to date • See also our Prompt Photon Paper: arXiv:1012.4389 [hep-ex], Talk by Sergei Chekanov

  29. Searches for excited quarks (1/1) • Search for decay of excited quarks in two partons, i.e. q*jj signatures • Looked for di-jet resonance in the measured Mjj distribution • leading jet pt>150 GeV • Mjj>350GeV • spectrum compatible with a smooth monotonic function • Published exclusion limit superseded all previous experiments • 0.5<M(q*)<1.53 TeV excluded at 95% C.L. • Experimental systematic uncertainties included: JES (dominant), background fit, luminosity.

  30. Heavy Ions (1/1) • Heavy Ions run in 2010 • lead-lead collisions • nucleon-nucleon centre of mass energy √s = 2.76 TeV • Collisions of heavy ions at ultra-relativistic energies are expected to produce quark gluon plasma • Jet Quenching • First observation of an enhancement of events with large dijet asymmetries

  31. Content • ATLAS Detector and Data Taking • Detector Performance • Highlights of the 2010 Physics Results • Prospects and Conclusion • Summary • Excellent performance of ATLAS detector • Subsystems operating according to design specifications • High data-collection efficiency • Monte Carlo simulation in good agreement with data • Many Interesting physics results already published • Hope to see something new in 2011