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Status of ATLAS experiment by hedongchenchen


									Status of ATLAS experiment

    On behalf of the ATLAS collaboration
           LHC     p-p collisions at √s=14TeV
                  2 1
Ldes  10 cm s
                              bunch crossing every 25 ns (40 MHz)

  Large Hadron Collider
                                                  Lake of Geneva


                ALICE                 ATLAS
Temperature of superconducting magnet 1.9 K (2.3 for CMBR)
 Assuming the machine can be operated for 200 days per year and assuming the
luminosity lifetime of 15 hours maximum total integrated luminosity per year of
~ 100 fbˉ¹
Physics at the LHC s at
corresponds to conditions
around here
                 • 25m diameter
Basic numbers:
                 • 46m total length
                 • 7000t weight
                 •~ 3000 km of cables
                 • installed just across the CERN
                 main site, 92 meters below
                 • ATLAS cavern: 55m long, 32m
                 wide, 35m high: just large enough
                 for the detector – ‘ship in a bottle’,
                 but have to assemble in situ

                                            Main surface
                                            building SX1

                             Control room
ATLAS has over 2000 scientists and engineers from 37
countries and 167 institutions, 550 MCHF.
First beam event in ATLAS
10th of September
First beam event in ATLAS
    10th of September
  Detector components …
                                 4 super-conducting magnets: solenoid + 3 toroids
  Silicon Pixel detector       Solenoid field 2T in inner detector region
                               toroid field peak strength 4T
 80 M channels, intrinsic
                                                                            TileCal hadronic calorimeter
 resolution 10 x 110 μm

 Silicon tracker
                                                                                      structure: iron
                                                                                      absorber +
~ 6 ∙106 channels                                                                     scintillator tiles
80 μm wide strips                                                                     ~ 10000
  Radiation Tracker                                                            Muon spectrometer

  Xe field straw tubes,                                                       ~1200 precision chambers
  electron – pion separation          LAr calorimeters (EMC, HC)              for track reconstruction
                                     ~ 160000 + 10000 channels                ~600 RPC and ~3600
  ~ 35 hits/track for track          (EMC,HC)                                 TGC trigger chambers
                                        10%/√E energy resolution for e,γ      Stand-alone momentum
                                     Trigger for electrons, photons and       re-solution Δpt/pt < 10%
                                     jets                                     up to 1 TeV
Base characteristics
• Tracking (||<2.5, B=2T) :
     -- Si pixels and strips
     -- Transition Radiation Detector (e/

•   Calorimetry (||<5) :
   -- EM : Pb-LAr
   -- HAD: Fe/scintillator (central), Cu/W-LAr (fwd)

•   Muon Spectrometer (||<2.7) :
   air-core toroids with muon chambers
Installation – the years 2003 to 2007 …

                   • All material lowered thru 2
                   shafts, Ø 12 and 18m

                                       Jun 2007
                            • Heaviest piece of
                                     280 t
                            • ‘Ballet’ of logistics
                            at the ATLAS site


                                        Dec 2004       Dec2005
Current understanding of the performance of
ATLAS detector is based on the analysis of :

 Full simulation of the different processes
 Test beam data
 Calibration runs in each subsystem
 Cosmic runs
                                         SCT: 4 cylindrical double layers (one axial
  Inner detector                         and one with a stereo angle of 40 mrad) of
                                         barrel silicon-microstrip sensors layers with
  Pixels : 3 layers with                 R=30,37,44, 51 cm 6 M channels
  R=5, 8 and 12 cm
  intrinsic resolution 10 x
  110 μm
  80 M channels

TRT: 4 mm straw tubes, arranged
in 2∙160 disks and 73 layers,
40 K channels
•Double purpose: Enhanced
pion-electron separation (TR γ’s
convert into e’s in Xe) , track
determination (average 35
hits/track, single tub res. 130
μm))                                              TRT/SCT installed Aug 2006
                                                    Pixel installed June 2007

                       /pT ~ 5x10-4 pT  0.01
                                            Cosmic event in TRT, 23 August 08.

                                                  Rejection of light jets and
                                                  cjets versus b-jet
                                                  efficiency for t tbar events.

. Current status:
Pixels: 3 leaky cooling loops in End Cap
(12 modules per loop).
 tested only a few days in April
2008,interrupted by cooling plant incident.
SCT: Defective channels – 1.2 % (0.7 % in
TRT:Switch to Xenon based mixture of
Xe/CO2/O2 (Xe provides Transition
Radiation features = particle identification)
around September 15.
Dead channels 1.2-2.0%, delivery of
some readout elements being completed
run with Xenon or not – to be decided
                        LAr and Tile Calorimeters

                                                Tile barrel     Tile extended barrel

LAr hadronic
end-cap (HEC)

LAr EM end-cap (EMEC)

                              LAr EM barrel

                                                              LAr forward calorimeter (FCAL)
  LAr calorimeters
Uses accordion-shaped electrodes
  and lead (in barrel) absorbers
 Electromagnetic Calorimeter
 barrel,endcap: Pb-Lar
 ~10%/√E energy resolution e/γ
 Hadron Calorimeter
 barrel Iron-Tile EC/Fwd Cu/W-
  LAr (~20000 channels)
 /E ~ 50%/E  0.03 pion (10 )
                   Since May 2008
    full calorimeter up, integrated in DAQ, slow
      Expected performance and current status
Overall reconstruction and
identification efficiency of
various levels of electron
cuts: loose, medium, and
tight isol. as a function of ET
for single electrons (open
symbols) and for isolated
electrons in a sample of
physics events with a busy

        Current status: 729 of 173312 channels dead (0.4%): no
        physics/calibration pulses , dominated by failing optical links
        • 0.3% channels with calibration problems, corrections implemented
    Hadronic Tile calorimeter
      scintillating tiles + iron absorbers, ΔE/E = 50%/√E  3%

Installation in the
cavern                                          
 Ext. Barrel C December                             
 Barrel      October 2005
 Ext. Barrel A May 2006
    Current status
From M8
Over about 5k cells, 10k channels:
43 masked cells (two drawers)
20 cells have one masked channel
(information can be recovered using the
other channel)

Status on 12-Sep:                             Tile Cal was the first
Three drawers do not send data                subsystem in cosmic runs
One drawer is unstable (need to cycle
power from time to time)
Two drawers send some %% of corrupted
Total number of affected cells is ~100 - 2%
(but not in all events)

We are within the 5% of failures needed for
expected Missing ET reconstruction
              Muon Spectrometer -- Barrel
 Muon barrel has ~ 650 individual stations, arranged in 3
  concentric circles. Dual purpose: track reconstruction
  (resolution 50μm/station → Δpt/pt < 10% up to 1 TeV)
  and (level-1) trigger
Barrel stations consist of a Monitored Drift Chamber
   (MDT), built from 3 cm drift tubes, and equipped with
   a optical monitoring system to reconstruct chamber
    Resistive Plate Chambers (RPC) in the middle and
   outer layer, operated in proportional mode for
MDT -RPC Correlation
  (cosmics data)
             Muon Spectrometer -- Endcap
~600 MDT and 64 CSC
(Cathode Strip Chambers)
precision chambers for
 1578 Thin Gap Chambers
(TGCs) as trigger: multi-wire
proportional chambers, wire
spacing 1.8 mm, operated with
n-pentane/CO2 mixture
 Geometry: 2 Small (movable),
2x4 Big (movable) and 2 Outer
Wheels, interconnected by
optical alignment system

                                Forward muon spectrometer
                                - ‘Big Wheels’ are all installed
Current status
   MDT – All Services Connected (1 ½ chambers out)
    ◦ EE chambers installed later
   TGC – Fully Installed (0.3% dead)
   RPC – Fully Installed (very few dead channels)
   CSC – hardware installed
    ◦ ROD firmware – being worked on
   Alignment System 99% operational
    ◦ A few blocked optical lines
     Trigger and Data Acquisition

The ATLAS Trigger and Data Acquisition is based on a three-level hierarchy
designed to reduce the data rate from 10’s PetaBytes/sec produced by
ATLAS to ~100 MegaBytes/sec of interesting physics

                                     Level 1 decision based on data
                                     from calorimeters and muon
                                     trigger chambers; synchronous
                                     at 40 MHz

                                     Level 2 uses Regions of Interest
                                     identified by Level-1 (< 10% of full
                                     event) with full granularity from
                                     all detectors

                                     Event Filter has access to full
                                     event and can perform more
                                     refined event reconstruction
          Event data flow from online to
    We are going to collect raw data               Ballon (30 km)
    at 320 MB/s for 50k seconds/day          CD stacks with
    and ~100 days/year                       1 year LHC data (~
    RAW dataset: 1.6 PB/year                 20 km )

Processing these events will require
~10k CPUs full time                      Concord
                                         (15 km)
At least 10k CPUs are also needed for
continuous simulation production of at    Mt.Blanc
                                           4.8 km
least 20-30% of the real data rate and
for analysis
There is no way to concentrate all
needed computing power and
storage capacity at CERN.The
LEP model will not scale to this         50 CD-ROM -> 36 GB -> 6 cm
                The ATLAS Distributed Computing
                     hierarchy (GRID) :
1 Tier-0 centre: CERN
10 Tier-1 centres: BNL(Brookhaven,
   CC-IN2P3 (Lyon, FR), FZK
   (Karlsruhe, DE), RAL (Chilton,
   UK), PIC (Barcelona, ES),CNAF
   (Bologna, IT), NDGF(DK/SE/NO),
   TRIUMF (Vancouver, CA), ASGC
   (Taipei, TW)
  ~35 Tier-2 facilities, some of them
    geographically distributed, in most
    participating countries
  ◦ Tier-3 facilities in all participating
   “Online”

   1. Commissioning of individual       subsystems in pit (almost finished)
   2. Integration of subsystems into ATLAS trigger and DAQ system (on-going)
   Several global commissioning runs using cosmic rays in 2008:
    ◦ - operate the whole experiment
    ◦ - achieve stable running for long periods
    ◦ - exercise Trigger and DAQ
    ◦      (data flow, run control, configuration)
    ◦ - operate control room as if data taking
   Should not forget “Offline”
   - Full Dress Rehearsal (FDR):
       a “stress test” of the full data processing and analysis chain from point-1
       to the end user
     Looking ahead: Commissioning
              with beam
   Cosmic triggers
    ◦ Exercise whole system, HLT, read out, TTC system,
    ◦ Alignment data, coarse timing, synchronisation,
    ◦ Monitoring, exercise reconstruction/ Tier 0
         efficient for barrel

   Single beam triggers (beam-gas, beam halo muons)
    ◦ End-cap detector timing & response
    ◦ High energy showers for more precise pulse shape

   Then collisions !
    ◦ Understanding of full detector, high statistics
    ◦ Increasing precision
In-situ calibrations
                         Initial  Ultimate        Samples
   e/γ E scale           ~ 2%     0.1 %          Z-> ee, J/ψ
   e/γ uniformity       1-2 %     0.5 %           Z-> ee
   Jet E scale            5-10 % ~ 1% W->jj in tt,W/Z +jets
   Tracking alignment 10-50 µm < 10 µm          tracks, Z->µµ
   Muon alignment 100-200 µm 30 µm         inclusive µ, Z->µµ

                                    Overall uniformity of energy
                                    response of EM calorimeter
                                    as a function of the number
                                    of events or as a function of
                                    the luminosity.
      Preparing to the physics
           (CSC notes)
 The most important at the first time
  topics were selected and studied
 Now the analysis is finished
 In total: ~80 notes, ~ 2.000 pages
 TDR + archive: Collect the notes into a
  CSC book and submit them to the hep-
   The LHC Physics Program has
    breakthrough discovery potential
   ATLAS is ready for data taking
   We are really excited with the physics
    starting soon!

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