ATLAS in the LHC collision era M.Bosman IFAE - Barcelona on behalf of the ATLAS Collaboration IMFP 2010 – La Palma

ATLAS, M.Bosman, IFAE2 1/2/2010 Effort of the ATLAS Worldwide Scientific Community for > 20 years ~ 2900 scientists (~1000 students), 172 Institutions, 37 countries

ATLAS, M.Bosman, IFAE3 1/2/2010 ATLAS Detector 45 m 24 m 7000 T

ATLAS, M.Bosman, IFAE4 1/2/2010 Silicon pixels (Pixel): channels Silicon strips (SCT) : channels Transition Radiation Tracker (TRT) : straw tubes (Xe), channels e/  separation  /p T ~ 5x10 -4 p T  0.01 Inner Detector Tracking |  |<2.5 B=2T

ATLAS, M.Bosman, IFAE5 1/2/2010 Calorimetry Electromagnetic Calorimeter barrel,endcap: Pb-LAr ~10%/√E energy resolution e/γ channels: longitudinal segmentation Calorimetry |  |<5 Hadron Calorimeter barrel Iron-Tile EC/Fwd Cu/W-LAr (~20000 channels)  /E ~ 50%/  E  0.03 pion (10 ) Trigger for e/γ, jets, Missing E T

ATLAS, M.Bosman, IFAE6 1/2/2010 Muon System Stand-alone momentum resolution Δpt/pt < 10% up to 1 TeV ~1200 MDT precision chambers for track reconstruction (+ CSC) ~600 RPC and ~3600 TGC trigger chambers 2-6 Tm |  |< Tm 1.6<|  |<2.7

ATLAS, M.Bosman, IFAE7 1/2/2010 People are happy again... A key date for ATLAS in 2009

ATLAS, M.Bosman, IFAE8 1/2/2010 LHC went very quickly from circulating beams to collisions at √s = 900 GeV Monday 23 November: first collisions at √s = 900 GeV !  ATLAS records ~ 200 events  (first one observed at 14:22) Friday 20 November: Circulating beams  “Beam splashes”

ATLAS, M.Bosman, IFAE9 1/2/2010 Sunday 6 December: machine protection system commissioned  stable (safe) beams for first time  full tracker at nominal voltage  whole ATLAS operational

ATLAS, M.Bosman, IFAE10 1/2/2010

ATLAS, M.Bosman, IFAE11 1/2/2010 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 ~ events

ATLAS, M.Bosman, IFAE12 1/2/2010 ■ 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 Detector is fully operational

ATLAS, M.Bosman, IFAE13 1/2/2010 Let’s go back in time..... Cosmic Muon Runs  216 Million Cosmics in Sep/Oct 2008  90 Million Cosmics in Jun/Jul 2009  266 Million Cosmics in Oct/Nov 2009

ATLAS, M.Bosman, IFAE14 1/2/2010 Cosmics-Muon-Runs useful for initial detector calibration, operation experience,... some examples Cosmic Muon Runs alignment of SCT efficiency of MDT tubes 2008 Cosmics Data

ATLAS, M.Bosman, IFAE15 1/2/2010 Cosmics-Muon-Runs useful for initial detector calibration, operation experience,... a couple of examples Beam Splashes Calorimeter energy calibration E T Level-1 trigger versus offline reconstruction Muon Chambers Timing Synchronize all chambers at a given z using the synchronous front of splash particles and the very large particle flux Calorimeter Timing After 2008 beam-splash data taking and analysis of many millions of cosmics events, timing good within a few ns

ATLAS, M.Bosman, IFAE16 1/2/2010 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 ~ 34k ≈ 1 μb -1 Average data-taking efficiency: ~ 90% Recorded data samples

ATLAS, M.Bosman, IFAE17 1/2/2010 Max peak luminosity seen by ATLAS : ~ 7 x cm -2 s -1 Measuring luminosity example: run with 4hours of stable beam scintillators in front of endcap forward luminosity monitor (22 m / in front of quadrupole) LAr endcaps overall systematic uncertainty up to 30%. ramping-up Silicon Detector after stable-beam signal

ATLAS, M.Bosman, IFAE18 1/2/2010 Dataflow EB High Level Trigger LVL2 ROS LVL1 Det. R/O Trigger DAQ 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 Trigger/DAQ Architecture 140M Channels

ATLAS, M.Bosman, IFAE19 1/2/2010 Scintillators (Z~± 3.5 m): rate up to ~ 30 Hz Collision trigger (L1) High-Level Trigger in rejection mode (in addition, running > 150 chains in pass-through) Spot size ~ 250 μm Online determination of the primary vertex and beam spot using L2 trigger algorithms Trigger

ATLAS, M.Bosman, IFAE20 1/2/2010 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 20 th November ■ ~ 8h between Data Acquisition at the pit and data arrival at Tier2 (including reconstruction at Tier0) ■ increasing usage of the Grid for analysis Worldwide data distribution and analysis

ATLAS, M.Bosman, IFAE21 1/2/2010 Collisions - Inner Detector

ATLAS, M.Bosman, IFAE22 1/2/2010 p K π 180k tracks Inner Detector - Pixel The dE/dx is measured per track as the mean of the cluster charge properly weighted for the track length in silicon. 180k tracks (3 Pixel Hits)  10% of data Track momentum X charge Q Pixel cluster width as a function of the track incident angle in Rphi direction

ATLAS, M.Bosman, IFAE23 1/2/2010 Inner Detector - SCT Lorentz angle extracted from the cluster-size vs angle compared to model prediction. Silicon strips Intrinsic module efficiency for tracks measured in the SCT Barrel (dead modules and chips are taken into account).

ATLAS, M.Bosman, IFAE24 1/2/2010 Inner Detector - TRT Transition Radiation Tracker Transition radiation intensity is proportional to particle relativistic factor γ=E/mc 2. Onset for γ ~ 1000 Foil Anode wire Xe straw HV -  Energy of TR photons (proportional to  1 -  2 ): ~ keV (X-rays)  Many crossings of polypropylene foils (radiator) to increase TR photons  Xenon as active gas for high X-ray absorption electron from photon conversion reconstructed in ID with tight identification in calorimeter all tracks

ATLAS, M.Bosman, IFAE25 1/2/2010 Reconstructing decays p T (track) > 100 MeV MC signal and background normalized independently

ATLAS, M.Bosman, IFAE26 1/2/2010 Reconstructing decays K0SK0S Λ

ATLAS, M.Bosman, IFAE27 1/2/2010 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   e + e - conversions

ATLAS, M.Bosman, IFAE28 1/2/2010 Calorimeter – cell signals cell signal in randomly triggered events LAr calorimeter cell signal in collision events

ATLAS, M.Bosman, IFAE29 1/2/2010 Data and MC normalised to the same area Calorimeter – photons : 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 applied π 0  γγ

ATLAS, M.Bosman, IFAE30 1/2/2010 Soft photons ! Challenging because of material in front of EM calorimeter (cryostat, coil): ~ 2.5 X 0 at η=0 Calorimeter – photons Photon candidates: shower shape in the EM calorimeter

ATLAS, M.Bosman, IFAE31 1/2/2010 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) Calorimeter – Electron candidates

ATLAS, M.Bosman, IFAE32 1/2/2010 Good agreement in the (challenging) low-E region indicates good description of material and shower physics in Geant4 simulation Years of test-beam, collaboration with Geant4 team |η| < 0.8, 0.5 < p T < 10 GeV Cluster energy at EM scale Monte Carlo and data normalized to same area Calorimeter – Isolated hadron response

ATLAS, M.Bosman, IFAE33 1/2/2010 Calorimeter - Jets Jets √s=2.36 TeV √s=900 GeV

ATLAS, M.Bosman, IFAE34 1/2/2010 Uncalibrated EM scale jets with pT>7 GeV Monte Carlo (Non Diffractive Minimim Bias) normalized to number of jets or events in data Events with2 jets with p T > 7 GeV Calorimeter - Jets

ATLAS, M.Bosman, IFAE35 1/2/2010 ■ 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, ~ cells) METy METx / METy = x/y components of missing E T vector METx Calorimeter – Missing Transverse Energy

ATLAS, M.Bosman, IFAE36 1/2/2010 METx Calorimeter – Missing Transverse Energy

ATLAS, M.Bosman, IFAE37 1/2/2010 Collisions: a physics Roadmap time Test beam, cosmic runs, pre-alignment & calibration, extensive simulations... Search for very striking new physics signature Use SM processes as “standard candles” Initial detector & trigger synchronisation, commissioning, calibration & alignment, material Sensitivity to TeV resonances → lepton pairs Understand SUSY and Higgs background from SM More accurate alignment & EM/Jet/ETmiss calibration Higgs discovery sensitivity (M H =130~500 GeV) Explore SUSY to m ~ TeV Precision SM measurements Integrated Luminosity (a.u.)

ATLAS, M.Bosman, IFAE38 1/2/2010 Example of first signals 1 pb -1  3 days at at 30% efficiency ATLAS J/  Y 1S After all cuts: ~ 5000 (800) J/  (Y)  / L = cm -2 s -1 (for 30% machine x detector data taking efficiency) (at 7 TeV reduced by ~x2)  tracker momentum scale, trigger performance, detector efficiency, sanity checks, … 50 pb -1 After all cuts: ~ 160 Z  ee  day at L = cm -2 s -1 energy/momentum scale of full detector Muon Spectrometer alignment, lepton trigger and reconstruction efficiency, … ~25 k events for 50 pb -1 at 14 TeV (at 7 TeV reduced by ~x2) quickly dominated by systematic Initial robust analysis e10 trigger loose identification background extrapolated from side bands 14 TeV

ATLAS, M.Bosman, IFAE39 1/2/2010 W/Z Production W  Trigger and offline efficiencies from tag- and-probe (Z  ) Muon isolation in calo Missing E T > 25GeV  Ldt=50pb -1 : 300k W, 20k bckgd events Z  Trigger and offline eff. from tag-and-probe Tracks in Muon Spectrometer  L dt = 50pb -1 : 26k Z, 0.1k bckgd evt ATLAS 14 TeV at 7 TeV, about a factor 2 less signal events ATLAS

ATLAS, M.Bosman, IFAE40 1/2/2010 ttbar pair production: semi leptonic decays Top production 1 jet p T > 20 GeV 3 jets pT> 40 GeV + P T (lep) > 20 GeV Missing E T > 20 GeV No b-tagging for 200 pb-1  channel 1600 events Signal, 800 Bck e channel: 1300 events Signal, 600 Bck 10 TeV at 7 TeV, signal reduced by factor 2.5

ATLAS, M.Bosman, IFAE41 1/2/2010 ■ 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. Conclusions taken from F.Gianotti, ATLAS Spokesperson Report to CERN Council Dec 09