Collider Physics Mini-Workshop Taipei July 21 Ashfaq Ahmad
ATLAS Experiment at the LHC
Ashfaq AhmadInstitute of PhysicsAcademia Sinica
Introduction to ATLAS Physics motivationATLAS Combined Test beamCommissioningSummary
Ashfaq Ahmad
Diameter: 25 mBarrel toroid length: 26 mLength: 46 mOverall weight: 7000 Tons
ATLAS: A Toroidal Lhc ApparatuS
Multi purpose particle detector
(coverage up to |η|=5, L=1034 cm-2s-1)
Tracking (|η|<2.5, B=2T):Si pixels and stripsTransition Radiation Detector (e/π separation)
Calorimetry (|η|<4.9):LAr EM Calo: (|η|<3.2)HAD Calo: (|η|<4.9)scintillator-Tile (barrel), LAr (fwd)
Muon Spectrometer (|η|<2.7):Air-core toroids(B~0.5T) with muon chambers
p, 7TeVp, 7TeV
Collider Physics Mini-Workshop Taipei July 21 Ashfaq Ahmad
60 m92 m
ATLAS superimposed to the 5 floors of building 40
Atlas assembled 92 mbelow ground at CERN
Scale of ATLAS
Collider Physics Mini-Workshop Taipei July 21 Ashfaq Ahmad
Event rate
Reconstructed tracks with pt > 25 GeV
At high luminosity event rate ~ 1GHzSpace between two bunches is 25ns~7.5mOn average 23 minimum bias inelastic event low pT
events per bunch crossing of 25ns
Pile up: H →ZZ →4µ
Reconstructed tracks for pT >25GeV
Collider Physics Mini-Workshop Taipei July 21 Ashfaq Ahmad
Status(Atlas Cavern)
Installation of Barrel Toroidswill finish next month(Aug05)
LAr and Tile Barrel Calorimeters are in the pit
Collider Physics Mini-Workshop Taipei July 21 Ashfaq Ahmad
Basic Detector Components
Photons
e±
muons
Π± , p
neutrons
Innermost Layer …Outermost Layer
Trackingdetector
Electromagneticcalorimeter
Hadroniccalorimeter
Muonchambers
Collider Physics Mini-Workshop Taipei July 21 Ashfaq Ahmad
Inner Detector (ID)The Inner Detector (ID) has three sub-systems:
Pixels (0.8 108 channels)
Silicon Tracker (SCT)(6 106 channels)
Transition Radiation Tracker (TRT)
(4 105 channels)
Radiation tracker : TRT
6m long, 1.1 m radius
Si strips tracker : SCTPixels
Precision Tracking: Pixel and SCTContinuous Tracking and e identification: TRTID inside 2 Tesla solenoid field
Collider Physics Mini-Workshop Taipei July 21 Ashfaq Ahmad
LAr and Tile CalorimetersTile barrel Tile extended barrel
LAr forward calorimeter (FCAL)
LAr hadronic end-cap (HEC)
LAr EM end-cap (EMEC)
LAr EM barrel
Collider Physics Mini-Workshop Taipei July 21 Ashfaq Ahmad
Muon Spectrometer
Precision chambers:- MDTs in the barrel and end-caps- CSCs at large rapidity for the
innermost end-cap stationsTrigger chambers:- RPCs in the barrel- TGCs in the end-caps
The Muon Spectrometer is instrumented with precision chambers and fast trigger chambers
Collider Physics Mini-Workshop Taipei July 21 Ashfaq Ahmad
Physics Motivation (i)
What gives particle mass?The missing piece of the SM is the Higgs (H)Breaks electroweak symmetryGenerates masses of particles
Higgs properties predicted-except its mass
From LEP direct search:MH > 114.4 GeV
From Electroweak fit of the SM:MH < 260 GeV
MH < 1.2 TeV else WW scattering violates unitarity
If SM is correct and there is Higgs then it can be observed at the LHC(ATLAS/CMS)
The LHC experiments have to coverFrom the LEP limit up to the TeV scale
Collider Physics Mini-Workshop Taipei July 21 Ashfaq Ahmad
Standard Model Higgs Production At LHCExcluded by LEP M. Spira, Fortsch. Phys. 46 (1998) 203.
Direct:Gluon Fusion
AssociatedProduction(tt or bb):Small σ
AssociatedProduction(W or Z):Small σ
Vector BosonFusion (VBF):Distinct FinalState
Collider Physics Mini-Workshop Taipei July 21 Ashfaq Ahmad
Standard Model Higgs Decay
Bra
nchi
ng R
atio
(Hig
gs)
Low mass range ~2 Mz
H →γγ : smallest BR but better resolution
H →bbar : good BR but poor resolution (15%)
Intermediate mass
H →WW*,ZZ*, useful at MH >125GeV
For MH >2 MZ
W decays to jets or lepton + neutrino
Search Channel depends on MH
Collider Physics Mini-Workshop Taipei July 21 Ashfaq Ahmad
Overall View of the SM Higgs
5σ observation is possible for 30 fb-1 (in first year(s) at low luminosity operation)
Observation of all channels important to extract convincing signal in first year
5σ
ATLAS30 fb-1
Collider Physics Mini-Workshop Taipei July 21 Ashfaq Ahmad
Physics Motivation (ii)
SUSY search at LHCunification matter-forces/fermions-bosons is beautifulallows incorporation of gravityallows unification of forces at GUT scaleprovides candidate for cold dark matternot ruled out by present datapredicts light Higgs as favored by data
Exotics: extra dimension, black holes production…
Collider Physics Mini-Workshop Taipei July 21 Ashfaq Ahmad
Testing the detector, Combined Test Beam (2004)
Collider Physics Mini-Workshop Taipei July 21 Ashfaq Ahmad
The ATLAS Combined Test BeamFull “vertical slice” of ATLAS tested on CERN H8 beam line May-November 2004
x
z
y
Geant4 simulated layout of the test-beam set-
up
For first time, all ATLAS sub-detectors integrated and run together with commonDAQ, “final” electronics, slow-control, etc. Gained lot of global operation experience during ~ 6 month run. Common ATLAS software used to analyze the data
Collider Physics Mini-Workshop Taipei July 21 Ashfaq Ahmad
TRT LAr
Tilecal
MDT-RPC
End-cap Muon chambers
~ 90 million events collected ~ 4.5 TB of data:e±, π ± 1 → 250 GeVµ ±, π ±, p up to 350 GeVγ ~ 30 GeV B-field = 0 → 1.4 T
Collider Physics Mini-Workshop Taipei July 21 Ashfaq Ahmad
Validating detector simulation at the CTBE = 100 GeV
σ = 16 µmSimulated data,
σ = 17 µm
Simulated data,σ = 23 µm
E = 180 GeVσ = 22 µm
Pixels
SCT
ATLAS preliminary
Collider Physics Mini-Workshop Taipei July 21 Ashfaq Ahmad
Detector calibration using CTB data
From the CTB data maps of dead/noisy straws are createdAlgorithms are in place to register maps in the databaseDuring the reconstruction straw status is read from the Condition databaseBad channels are masked, hence not used in reconstruction chain
180GeV electrons without magnetic field
Application of dead/noisy straws data
Collider Physics Mini-Workshop Taipei July 21 Ashfaq Ahmad
Step 1 : Cosmics run : end 2006-March 2007 commissioning at sub-detector level has startedhere “physics data” are cosmic muonsGood for the calibration and alignment of detectorAtlas has already started recording cosmic muons!
For now TileCalo, article in Nature on 14 July 2005:http://www.nature.com/nphys/journal/vaop/nprelaunch/full/nphys005.html
Step 2 : Only one beam in the machine : April-May 2007 ?here “physics data” are beam-halo muons and beam-gas events
Step 3 : First pp collisions : prepare the trigger and the detector
Step 4 : Commissioning of physics (e.g. understand backgrounds to discovery channels) can start ...
ATLAS Commissioning with “physics data”
Collider Physics Mini-Workshop Taipei July 21 Ashfaq Ahmad
ATLAS Commissioning~ 5 million cosmic ~ 5 million cosmic muonsmuons
enter the cavern in 15 minutesenter the cavern in 15 minutes First cosmic event in AtlasFirst cosmic event in Atlas
Tower energies:~2.5 GeV
Collider Physics Mini-Workshop Taipei July 21 Ashfaq Ahmad
Contribution from our groupHardware:
Provided opto links for Pixel, SCT, LAr and Tile (In fact we are giving “light” to Atlas!)
LMT for the SCTSoftware:
One of our colleague is Atlas software release coordinatorTaking care of smooth and useful release buildsProvided monitoring software for the TRT and global ID level inside Athena framework
Useful for debugging detector, spotting dead/noisy channels, studying correlations among sub-detectors…..
Grid:To deal with the enormous amount of data (Atlas ~ 1PB per year) produced by the LHC, Grid is essentialOur group is taking active part in the development, deployment and testing of the Grid (releases)Contributed actively to DC1 and DC2After all we are Tier1!! (the only one in Asia so far)You can access/process LHC data while sitting at home institute (Great chance for new people to join and take part in the LHC analysis)
Collider Physics Mini-Workshop Taipei July 21 Ashfaq Ahmad
SummaryATLAS offers a wealth of physicsATLAS sub-detectors have passed extensive period of construction, R&D, TestbeamATLAS commissioning has started on sub-detector levelThe whole ATLAS commissioning in 2006-2007We are looking forward to first p-p collision in summer 2007
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