TPC%20Calibration%20with%20laser%20tracks

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TPC Calibrationwith laser tracks

• B.S. Nielsen G. Renault
• for the
• ALICE Collaboration
• Niels Bohr Institute

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Installation work on laser system

• Installation work still to be done
• Mount laser optics on TPC endcaps
• Build laser tent/hut in clean room
• Install laser (Spectron from Copenhagen or new
  Ekspla)
• Take care of operational safety
• Align all laser optics with UV beam --- this
  could be time consuming
• How to run the laser in the clean room
• DCS should work, but it is also possible to
  adjust by hand
• Laser free running (10 Hz) --- supply trigger
  like cosmics
• Operate each TPC half separately --- may have a
  fair amount of some setup time to change

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First steps at NBI

• What has been done?
• My Aliroot installed (soon on the HEHI www)
• Aliroot environment installed (Config.C)
• First SimulationReconstruction chain done
• What needs to be done?
• Simulate laser tracks in the TPC (in Aliroot)
• Reconstruct laser tracks in the TPC
• Extract drift velocity (Temperature gradient)
• Study misalignment effects on reconstructed laser
  tracks
• Man power (NBI) Johann, Gaël, Børge

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Back up
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Why do we needlaser tracks in the TPC?

• In order to align and calibrate the TPC with
  Straight tracks
• Correct distortions in the z-direction due to
• Temperature gradient (drift velocity gradient
  measurement)
• Mechanical misalignment (reconstructed straight
  tracks)
• Take into account
• Distortion due to ExB effects (calibration)
• Space-Charge in the drift volume (calibration)

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Laser tracks principle

• 2 g (24.66eV) impurity ionization
• N2(trace), IP5-8 eV
• Ne,CO2 (90/10), IP10eV
• Metal structures will emit
• photo-electrons

B
drift
y
E
x
laser track
z