1. ATLAS, 18-12-2009 1 ATLAS through first data Fabiola Gianotti (on behalf of the ATLAS Collaboration)

2. ATLAS, 18-12-2009 2 > 20 years of efforts of the worldwide ATLAS scientific community, supported by Funding Agencies and Governments Albany, Alberta, NIKHEF Amsterdam, Ankara, LAPP Annecy, Argonne NL, Arizona, UT Arlington, Athens, NTU Athens, Baku, IFAE Barcelona, Belgrade, Bergen, Berkeley LBL and UC, HU Berlin, Bern, Birmingham, UAN Bogota, Bologna, Bonn, Boston, Brandeis, Brasil Cluster, Bratislava/SAS Kosice, Brookhaven NL, Buenos Aires, Bucharest, Cambridge, Carleton, CERN, Chinese Cluster, Chicago, Chile, Clermont-Ferrand, Columbia, NBI Copenhagen, Cosenza, AGH UST Cracow, IFJ PAN Cracow, SMU Dallas, UT Dallas, DESY, Dortmund, TU Dresden, JINR Dubna, Duke, Edinburgh, Frascati, Freiburg, Geneva, Genoa, Giessen, Glasgow, Göttingen, LPSC Grenoble, Technion Haifa, Hampton, Harvard, Heidelberg, Hiroshima IT, Indiana, Innsbruck, Iowa SU, Iowa, UC Irvine, Istanbul Bogazici, KEK, Kobe, Kyoto, Kyoto UE, Lancaster, UN La Plata, Lecce, Lisbon LIP, Liverpool, Ljubljana, QMW London, RHBNC London, UC London, Lund, UA Madrid, Mainz, Manchester, CPPM Marseille, Massachusetts, MIT, Melbourne, Michigan, Michigan SU, Milano, Minsk NAS, Minsk NCPHEP, Montreal, McGill Montreal, RUPHE Morocco, FIAN Moscow, ITEP Moscow, MEPhI Moscow, MSU Moscow, Munich LMU, MPI Munich, Nagasaki IAS, Nagoya, Naples, New Mexico, New York, Nijmegen, BINP Novosibirsk, Ohio SU, Okayama, Oklahoma, Oklahoma SU, Olomouc, Oregon, LAL Orsay, Osaka, Oslo, Oxford, Paris VI and VII, Pavia, Pennsylvania, Pisa, Pittsburgh, CAS Prague, CU Prague, TU Prague, IHEP Protvino, Regina, Rome I, Rome II, Rome III, Rutherford Appleton Laboratory, DAPNIA Saclay, Santa Cruz UC, Sheffield, Shinshu, Siegen, Simon Fraser Burnaby, SLAC, NPI Petersburg, Stockholm, KTH Stockholm, Stony Brook, Sydney, Sussex, AS Taipei, Tbilisi, Tel Aviv, Thessaloniki, Tokyo ICEPP, Tokyo MU, Tokyo Tech, Toronto, TRIUMF, Tsukuba, Tufts, Udine/ICTP, Uppsala, UI Urbana, Valencia, UBC Vancouver, Victoria, Waseda, Washington, Weizmann Rehovot, FH Wiener Neustadt, Wisconsin, Wuppertal, Würzburg, Yale, Yerevan ~ 2900 scientists (~1000 students), 172 Institutions, 37 countries

3. ATLAS, 18-12-2009 3 Since 20 November: a fantastic escalation of events ….

4. ATLAS, 18-12-2009 4 Monday 23 November: first collisions at √s = 900 GeV !  ATLAS records ~ 200 events (first one observed at 14:22)

5. ATLAS, 18-12-2009 5 Sunday 6 December: machine protection system commissioned  stable (safe) beams for first time  full tracker at nominal voltage  whole ATLAS operational

6. ATLAS, 18-12-2009 6

7. 7 Jet1: E T (EM scale)~ 16 GeV, η= -2.1 Jet2: E T (EM scale) ~ 6 GeV, η= 1.4 8, 14, 16 December: collisions at √s = 2.36 TeV (few hours total)  ATLAS records ~ 34000 events at flat-top

8. ATLAS, 18-12-2009 8 Detector is fully operational ■ Pixels and Silicon strips (SCT) at nominal voltage only with stable beams ■ Solenoid and/or toroids off in some periods ■ Muon forward chambers (CSC) running in separate partition for rate tests Online detector control panel

9. ATLAS, 18-12-2009 9 Recorded data samples Number of Integrated luminosity events (< 30% uncertainty) Total ~ 920k ~ 20 μ b -1 With stable beams (  tracker fully on) ~ 540k ~ 12 μ b -1 At √s=2.36 TeV (flat top) ~ 34k ≈ 1 μ b -1 Average data-taking efficiency: ~ 90% Max peak luminosity seen by ATLAS : ~ 7 x 10 26 cm -2 s -1

10. ATLAS, 18-12-2009 10

11. ATLAS, 18-12-2009 11 Spot size ~ 250 μm Trigger Scintillators (Z~± 3.5 m): rate up to ~ 30 Hz Collision trigger (L1) Online determination of the primary vertex and beam spot using L2 trigger algorithms High-Level Trigger in rejection mode (in addition, running > 150 chains in pass-through)

12. ATLAS, 18-12-2009 WLCG 12 Worldwide data distribution and analysis MB/s per day Total data throughput through the Grid (Tier0, Tier-1s, Tier-2s) Beam splashes First collisions Nov.Dec. Cosmics End of data taking ■ ~ 0.2 PB of data stored since 20 th November ■ ~ 8h between Data Acquisition at the pit and data arrival at Tier2 (including reconstruction atTier0) ■ increasing usage of the Grid for analysis

13. ATLAS, 18-12-2009 13 Inner Detector p K π 180k tracks Pixels Silicon strips Transition Radiation Tracker Transition radiation intensity is proportional to particle relativistic factor γ =E/mc 2. Onset for γ ~ 1000

14. ATLAS, 18-12-2009 14 p T (track) > 100 MeV MC signal and background normalized independently K0SK0S Λ

15. ATLAS, 18-12-2009 15 γ  e + e - conversions e+e+ e-e- γ conversion point R ~ 30 cm (1 st SCT layer) p T (e + ) = 1.75 GeV, 11 TRT high-threshold hits p T (e - ) = 0.79 GeV, 3 TRT high-threshold hits

16. ATLAS, 18-12-2009 16 π 0  γγ ■ 2 photon candidates with E T ( γ ) > 300 MeV ■ E T ( γγ ) > 900 MeV ■ Shower shapes compatible with photons ■ No corrections for upstream material Data and MC normalised to the same area Note: soft photons are challenging because of material in front of EM calorimeter (cryostat, coil): ~ 2.5 X 0 at η =0

17. ATLAS, 18-12-2009 17 Jets √s=2.36 TeV √s=900 GeV

18. ATLAS, 18-12-2009 18 Uncalibrated EM scale Monte Carlo normalized to number of jets or events in data events with 2 jets p T > 7 GeV

19. ATLAS, 18-12-2009 19 Missing transverse energy ■ Sensitive to calorimeter performance (noise, coherent noise, dead cells, mis-calibrations, cracks, etc.) and backgrounds from cosmics, beams, … ■ Measurement over full calorimeter coverage (360 0 in φ, |η| < 5, ~ 200000 cells) METy METx / METy indicate x/y components of missing E T vector METx

20. ATLAS, 18-12-2009 20 Good agreement in the (challenging) low-E region indicates good description of material and shower physics in G4 simulation (thanks also to years of test-beam …) Shower width in strip units (4.5mm) Photon candidates: shower shape in the EM calorimeter | η| < 0.8, 0.5 < p T < 10 GeV Cluster energy at EM scale Electron candidates: transition radiation signal in TRT More comparisons data – simulation: fundamental milestone for solid physics measurements Monte Carlo and data normalized to same area

21. ATLAS, 18-12-2009 21 ■ ATLAS has successfully collected first LHC collision data. ■ The whole experiment operated efficiently and fast, from data taking at the pit, to data transfer worldwide, to the production of first results (on a very short time scale … few days). ■ First LHC data indicate that the performance of the detector, simulation and reconstruction (including the understanding of material and control of instrumental effects) is far better than expected at this (initial) stage of the experiment and in an energy regime ATLAS was not optimized for. ■ Years of test beam activities, increasingly realistic simulations, and commissioning with cosmics to understand and optimize the detector performance and validate the software tools were fundamental to achieve these results. ■ The enthusiasm and the team spirit in the Collaboration are extraordinary. Conclusions This is only the beginning of an exciting physics phase and a major achievement of the worldwide ATLAS Collaboration after > 20 years of efforts to build a detector of unprecedented technology, complexity and performance.

22. ATLAS, 18-12-2009 22 ATLAS cavern, October 2005

23. ATLAS, 18-12-2009 23 Hector Berlioz, “Les Troyens”, opera in five acts Valencia, Palau de les Arts Reina Sofia, 31 October -12 November 2009 Many thanks to the accelerator team for the excellent machine performance, for the impressive progress over a few days of operation, and for the very pleasant and constructive interactions with ATLAS

24. ATLAS, 18-12-2009 24 Back-up

25. ATLAS, 18-12-2009 25 Electron candidates EM clusters E T > 2.5 GeV matched to a track  783 candidates in 330k minimum-bias events Data and MC normalised to the same area According to MC: ■ Sample dominated by hadron fakes ■ Most electrons from γ -conversions E (cluster) / p (track) Good data-MC agreement for (soft !) electrons and hadrons E T spectrum Transition radiation hits in the TRT (transition radiation from electrons produces more high-threshold hits)

26. ATLAS, 18-12-2009 26 Inner Detector (|  |<2.5, B=2T): Si Pixels and strips (SCT) + Transition Radiation straws Precise tracking and vertexing, e/  separation (TRT). Momentum resolution:  /p T ~ 3.4x10 -4 p T (GeV)  0.015 Length : ~ 46 m Radius : ~ 12 m Weight : ~ 7000 tons ~10 8 electronic channels Muon Spectrometer (|  |<2.7) : air-core toroids with gas-based chambers Muon trigger and measurement with momentum resolution < 10% up to  E  ~ TeV EM calorimeter: Pb-LAr Accordion e/  trigger, identification and measurement E-resolution: ~ 1% at 100 GeV, 0.5% at 1 TeV HAD calorimetry (|  |<5): segmentation, hermeticity Tilecal Fe/scintillator (central), Cu/W-LAr (fwd) Trigger and measurement of jets and missing E T E-resolution:  /E ~ 50%/  E  0.03 3-level trigger reducing the rate from 40 MHz to ~200 Hz

27. ATLAS, 18-12-2009 27 LUCID at 17 m ZDC at 140 mALFA at 240 m Zero Degree Calorimeter (Data taking in 2009) ALFA: Absolute Luminosity for ATLAS (Installation in 2010) LoI for Forward Proton detectors at 220 and 420 m (AFP): ongoing ATLAS review Forward detectors Luminosity Cerenkov Integrating Detector (Phase 1 operational since 2008)

28. ATLAS, 18-12-2009 28 Jets Jet1: E T (EM scale)~ 16 GeV Jet2: E T (EM scale) ~ 6 GeV √s=2.36 TeV Jet1: E T (EM scale)~ 15 GeV Jet2: E T (EM scale) ~ 12.5 GeV √s=900 GeV Jet1: E T (EM scale)~ 37 GeV Jet2: E T (EM scale) ~ 37 GeV

29. ATLAS, 18-12-2009 Rejection factor of ~10 4 looking for space points in the Inner Detector at Level 2 trigger Beam injection, record collision events. HLT algos off. HLT active after LHC declares stable beam BPTX prescaled by x20 as input to L2 ~20

30. ATLAS, 18-12-2009 Dataflow EB High Level Trigger LVL2 ROS LVL1 Det. R/O TriggerDAQ 2.5  s ~40 ms Calo MuTrCh Other detectors L2P L2N RoI RoI data (~2%) RoI requests LVL2 accept (~ 3 kHz) SFO LVL1 accept (75 kHz) 40 MHz EF EFP ~4 sec EF accept (~0.2 kHz) ROD ROB SFI EBN EFN DFML2SVROIB 500 nodes 100 nodes 150 nodes 1800 nodes Infrastructure Control & Monitoring CommunicationDatabases ~100 nodes Architecture 140M Channels

31. ATLAS, 18-12-2009 31 charged particles The Transition Radiation detector (TRT) Transition radiation is emitted whenever a relativistic charged particle traverses the border between two media with different dielectric constants. TR intensity is proportional to the particle  -factor  for a given particle momentum p, electrons emit more TR than pions  TR detectors used for particle identification Radiator: Polypropylen foils (15  ) interleaved with straws Foil Anode wire Xe straw HV -  Energy of TR photons (proportional to  1 -  2 ): ~ 10-30 keV (X-rays)  Many crossings of polypropylene foils (radiator) to increase TR photons  Xenon as active gas for high X-ray absorption

32. ATLAS, 18-12-2009 32