ATLAS through first data Fabiola Gianotti (on behalf of the ATLAS Collaboration)

> 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

Since 20 November: a fantastic escalation of events ….

Monday 23 November: first collisions at √s = 900 GeV ! ATLAS records ~ 200 events (first one observed at 14:22)

Sunday 6 December: machine protection system commissioned stable (safe) beams for first time full tracker at nominal voltage whole ATLAS operational

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

Detector is fully operational Online detector control panel 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

Average data-taking efficiency: ~ 90% Max peak luminosity seen by ATLAS : ~ 7 x 1026 cm-2 s-1 Recorded data samples Number of Integrated luminosity events (< 30% uncertainty) Total ~ 920k ~ 20 μb-1 With stable beams ( tracker fully on) ~ 540k ~ 12 μb-1 At √s=2.36 TeV (flat top) ~ 34k ≈ 1 μb-1 Average data-taking efficiency: ~ 90%

In the following: few examples from large number of (preliminary) detector performance results obtained in only a few days ….

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

Worldwide data distribution and analysis 5/6/2018 Worldwide data distribution and analysis WLCG 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 20th November ~ 8h between Data Acquisition at the pit and data arrival at Tier2 (including reconstruction atTier0) increasing usage of the Grid for analysis 12

Inner Detector Silicon strips Pixels Transition Radiation Tracker π 180k tracks Pixels Transition Radiation Tracker Transition radiation intensity is proportional to particle relativistic factor γ=E/mc2. Onset for γ ~ 1000

MC signal and background normalized independently pT (track) > 100 MeV MC signal and background normalized independently K0S Λ

γ  e+e- conversions e- e+ γ conversion point R ~ 30 cm (1st SCT layer) pT (e+) = 1.75 GeV, 11 TRT high-threshold hits pT (e-) = 0.79 GeV, 3 TRT high-threshold hits

π0  γγ 2 photon candidates with ET (γ) > 300 MeV Shower shapes compatible with photons No corrections for upstream material Note: soft photons are challenging because of material in front of EM calorimeter (cryostat, coil): ~ 2.5 X0 at η=0 Data and MC normalised to the same area

Jets √s=2.36 TeV √s=900 GeV

events with 2 jets pT> 7 GeV Uncalibrated EM scale Monte Carlo normalized to number of jets or events in data

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 (3600 in φ, |η| < 5, ~ 200000 cells) METx METx METx / METy indicate x/y components of missing ET vector METy

More comparisons data – simulation: Photon candidates: shower shape in the EM calorimeter More comparisons data – simulation: fundamental milestone for solid physics measurements Electron candidates: transition radiation signal in TRT Shower width in strip units (4.5mm) Monte Carlo and data normalized to same area |η| < 0.8, 0.5 < pT < 10 GeV Cluster energy at EM scale 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 …)

Conclusions 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. 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.

ATLAS cavern, October 2005

Many thanks to the accelerator team for the excellent 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

Back-up

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

Length : ~ 46 m Radius : ~ 12 m Weight : ~ 7000 tons Muon Spectrometer (||<2.7) : air-core toroids with gas-based chambers Muon trigger and measurement with momentum resolution < 10% up toE ~ TeV Length : ~ 46 m Radius : ~ 12 m Weight : ~ 7000 tons ~108 electronic channels 3-level trigger reducing the rate from 40 MHz to ~200 Hz Inner Detector (||<2.5, B=2T): Si Pixels and strips (SCT) + Transition Radiation straws Precise tracking and vertexing, e/ separation (TRT). Momentum resolution: /pT ~ 3.4x10-4 pT (GeV)  0.015 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 ET E-resolution:/E ~ 50%/E  0.03 26

Zero Degree Calorimeter Forward detectors LUCID at 17 m ALFA at 240 m ZDC at 140 m Luminosity Cerenkov Integrating Detector (Phase 1 operational since 2008) 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 27 27 27

Jets √s=2.36 TeV √s=2.36 TeV √s=900 GeV Jet1: ET (EM scale)~ 15 GeV

Beam injection, record collision events. HLT algos off. HLT active after LHC declares stable beam Rejection factor of ~104 looking for space points in the Inner Detector at Level 2 trigger ~20 BPTX prescaled by x20 as input to L2

Architecture 150 500 nodes nodes 100 nodes 1800 nodes ~100 nodes 140M 5/6/2018 Trigger DAQ Calo MuTrCh Other detectors LVL1 40 MHz 2.5 ms Det. R/O 140M Channels LVL1 accept (75 kHz) ROD RoI High Level Trigger Dataflow LVL2 ~40 ms 150 nodes 500 nodes ROS RoI requests ROB ROIB L2SV RoI data (~2%) L2P L2N EB 100 nodes EBN DFM LVL2 accept (~3 kHz) SFI 1800 nodes ~4 sec EFN EF EFP EF accept (~0.2 kHz) SFO ~100 nodes Infrastructure Control & Monitoring Communication Databases

Foil The Transition Radiation detector (TRT) Xe straw charged particles 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 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 Radiator: Polypropylen foils (15 ) interleaved with straws