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ATLAS in the LHC collision era
M.BosmanIFAE - Barcelonaon behalf of the ATLAS CollaborationIMFP 2010 – La Palma
ATLAS, M.Bosman, IFAE 21/2/2010
Effort of the ATLAS Worldwide Scientific Community for > 20 years
~ 2900 scientists (~1000 students), 172 Institutions, 37
countries
ATLAS, M.Bosman, IFAE 31/2/2010
ATLAS Detector
45 m
24 m
7000 T
ATLAS, M.Bosman, IFAE 41/2/2010
Silicon pixels (Pixel): 0.8 108 channelsSilicon strips (SCT) : 6 106 channelsTransition Radiation Tracker (TRT) :
straw tubes (Xe), 4 105 channelse/ separation
/pT ~ 5x10-4 pT 0.01
Inner Detector
Tracking ||<2.5 B=2T
ATLAS, M.Bosman, IFAE 51/2/2010
Calorimetry
Electromagnetic Calorimeterbarrel,endcap: Pb-LAr~10%/√E energy resolution e/γ180000 channels: longitudinal segmentation
Calorimetry ||<5
Hadron Calorimeterbarrel Iron-Tile EC/Fwd Cu/W-LAr (~20000 channels)/E ~ 50%/E 0.03 pion (10 )
Trigger for e/γ , jets, Missing ET
ATLAS, M.Bosman, IFAE 61/2/2010
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 ||<1.3 4-8 Tm 1.6<||<2.7
ATLAS, M.Bosman, IFAE 71/2/2010
People are happy again...
A key date for ATLAS in 2009
ATLAS, M.Bosman, IFAE 81/2/2010
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, IFAE 91/2/2010
Sunday 6 December: machine protection system commissioned
stable (safe) beams for first time full tracker at nominal voltage whole ATLAS operational
ATLAS, M.Bosman, IFAE 101/2/2010
ATLAS, M.Bosman, IFAE 111/2/2010 Jet1: ET (EM scale)~ 16 GeV, η= -2.1Jet2: ET (EM scale) ~ 6 GeV, η= 1.4
8, 14, 16 December: collisions at √s = 2.36 TeV (few hours total)ATLAS records ~ 34000 events
ATLAS, M.Bosman, IFAE 121/2/2010
■ 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, IFAE 131/2/2010
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, IFAE 141/2/2010
Cosmics-Muon-Runsuseful for initial detector calibration, operation experience, ...
some examples
Cosmic Muon Runs
alignment of SCT efficiency of MDT tubes
2008 Cosmics Data
ATLAS, M.Bosman, IFAE 151/2/2010
Cosmics-Muon-Runsuseful for initial detector calibration, operation experience, ...
a couple of examples
Beam Splashes
Calorimeter energy calibrationET 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, IFAE 161/2/2010
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, IFAE 171/2/2010
Max peak luminosity seen by ATLAS : ~ 7 x 1026 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, IFAE 181/2/2010
Dataflow
EBHigh LevelTrigger
LVL2
ROS
LVL1Det.
R/O
Trigger
DAQ
2.5 s
~40 ms
Calo MuTrChOther detectors
L2P L2N
RoI
RoI data (~2%)
RoI requests
LVL2 accept (~3 kHz)
SFO
LVL1 accept (75 kHz)
40 MHz
EFEFP
~4 sec
EF accept (~0.2 kHz)
ROD ROD ROD
ROB ROB ROB
SFI
EBN
EFN
DFM
L2SVROIB500nodes
100nodes
150nodes
1800nodes
Infrastructure Control &Monitoring
Communication Databases
~100nodes
Trigger/DAQ Architecture
140M Channels
ATLAS, M.Bosman, IFAE 191/2/2010
Scintillators (Z~± 3.5 m):rate up to ~ 30 Hz
Collision trigger (L1)
High-Level Trigger in rejectionmode (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, IFAE 201/2/2010
WLCG
MB/sper day Total data throughput through the Grid (Tier0, Tier-1s, Tier-2s)
Beam splashes
First collisions
Nov. Dec.
Cosmics
End of datataking
■ ~ 0.2 PB of data stored since 20th 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, IFAE 211/2/2010
Collisions - Inner Detector
ATLAS, M.Bosman, IFAE 221/2/2010
p
K
π
180k tracks
Inner Detector - PixelThe 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, IFAE 231/2/2010
Inner Detector - SCT
Lorentz angle extracted from the cluster-size vs angle compared to model prediction.
Silicon stripsIntrinsic module efficiency for tracks measured in the SCT Barrel (dead modules and chips are taken into account).
ATLAS, M.Bosman, IFAE 241/2/2010
Inner Detector - TRTTransition Radiation Tracker
Transition radiation intensity is proportional to particle relativistic factor γ=E/mc2. Onset for γ ~ 1000
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
electron from photon conversion reconstructed in ID with tight identification in calorimeter
all tracks
ATLAS, M.Bosman, IFAE 251/2/2010
Reconstructing decays
pT (track) > 100 MeVMC signal and background normalized independently
-+0sK
ATLAS, M.Bosman, IFAE 261/2/2010
Reconstructing decays+p ,p
K0S
Λ
ATLAS, M.Bosman, IFAE 271/2/2010
e+
e-γ conversion pointR ~ 30 cm (1st SCT layer)
pT (e+) = 1.75 GeV, 11 TRT high-threshold hitspT (e-) = 0.79 GeV, 3 TRT high-threshold hits
e+e- conversions
ATLAS, M.Bosman, IFAE 281/2/2010
Calorimeter – cell signalscell signal in randomly triggered events
LAr calorimeter
cell signal in collision events
ATLAS, M.Bosman, IFAE 291/2/2010
Data and MC normalised
to the same area
Calorimeter – photons : π0 γγ
■ 2 photon candidates with ET (γ) > 300 MeV
■ ET (γγ) > 900 MeV
■ Shower shapes compatible with photons■ No corrections for upstream material applied
π0 γγ
ATLAS, M.Bosman, IFAE 301/2/2010
Soft photons !Challenging because of material in front of EM calorimeter(cryostat, coil): ~ 2.5 X0 at η=0
Calorimeter – photons
Photon candidates: shower shape in the EM calorimeter
ATLAS, M.Bosman, IFAE 311/2/2010
EM clusters ET > 2.5 GeV matched to a track 783 candidates in 330k minimum-bias eventsData 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
ET spectrum
Transition radiation hits in the TRT(transition radiation from electrons producesmore high-threshold hits)
Calorimeter – Electron candidates
ATLAS, M.Bosman, IFAE 321/2/2010
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
p(tracker)
ter)E(calorime
:hadrons Isolated
|η| < 0.8, 0.5 < pT < 10 GeV Cluster energy at EM scale
Monte Carlo and data normalized to same area
Calorimeter – Isolated hadron response
ATLAS, M.Bosman, IFAE 331/2/2010
Calorimeter - Jets
Jets
√s=2.36 TeV √s=2.36 TeV
√s=900 GeV
ATLAS, M.Bosman, IFAE 341/2/2010
Uncalibrated EM scale jets with pT>7 GeVMonte Carlo (Non Diffractive Minimim Bias)normalized to number of jets or events in data
Events with2 jets with pT> 7 GeV
Calorimeter - Jets
ATLAS, M.Bosman, IFAE 351/2/2010
■ Sensitive to calorimeter performance (noise, coherent noise, dead cells, mis-calibrations, cracks, etc.) and backgrounds from cosmics, beams, …■ Measurement over full calorimeter coverage (3600 in φ, |η| < 5, ~ 200000 cells)
METy
METx / METy = x/y components of missing ET vector
METx
Calorimeter – Missing Transverse Energy
ATLAS, M.Bosman, IFAE 361/2/2010
METx
Calorimeter – Missing Transverse Energy
ATLAS, M.Bosman, IFAE 371/2/2010
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 1-1.5 TeV resonances → lepton pairs
Understand SUSY and Higgs background from SM
More accurate alignment & EM/Jet/ETmiss calibration
Higgs discovery sensitivity (MH=130~500 GeV)
Explore SUSY to m ~ TeV
Precision SM measurements
Inte
gra
ted L
um
inosi
ty (
a.u
.)
1
10
100
ATLAS, M.Bosman, IFAE 381/2/2010
Example of first signals1 pb-13 days at 1031at 30% efficiency
ATLAS
J/
Y1S
After all cuts:~ 5000 (800) J/ (Y) / day @ L = 1031 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 = 1031 cm-2 s-1
energy/momentum scale of full detectorMuon 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, IFAE 391/2/2010
W/Z ProductionW Trigger and offline efficiencies from tag-and-
probe (Z) Muon isolation in calo Missing ET > 25GeV
Ldt=50pb-1: 300k W, 20k bckgd events
Z Trigger and offline eff. from tag-and-probe Tracks in Muon Spectrometer
Ldt=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, IFAE 401/2/2010
ttbar pair production: semi leptonic decays
Top production
1 jet pT> 20 GeV
3 jets pT> 40 GeV +
PT(lep) > 20 GeV
Missing ET > 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, IFAE 411/2/2010
■ 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.
Conclusionstaken from F.Gianotti, ATLAS Spokesperson Report to CERN Council Dec 09
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