TPC Distortions in the Transverse Plane:

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• TPC Distortions in the Transverse Plane
• An Update
• Jim Thomas

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A Mnemonic for Listing the Potential Distortions
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The List of Distortions in the Transverse Plane

• The list can be enumerated by surfaces
• Outer field cage corrections
• Inner field cage corrections
• Central membrane corrections
• End-wheel and pad-plane corrections
• Pad Row 13 corrections and other local
  electrostatic defects
• Rotation and miss-alignment of sectors with
  respect to their ideal locations
• Rotation of either TPC end-wheel with respect
  to its ideal location
• and by volume
• Space Charge corrections due to charge in the
  volume of the TPC
• Magnetic field corrections due to B fields in
  the volume of the TPC
• Twist of the TPC with respect to the magnetic
  field axis and/or the measured map
• General coordinate transformations
• A few additional items are listed for
  completeness. (These items affect the drift of
  the electrons in the Z direction but do not
  strongly affect the distortions in the transverse
  plane.)

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We think of our events like this
Data Taken June 25, 2000.
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Most of our events look more like this
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SpaceCharge from (all) events cause distortion
Radius / 5 cm
Z / 5 cm
Distortion
Radius
Z
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Model for the distortions

• Old Model
• Beam gas events leave a uniform deposition of
  charge in the TPC
• The charge from the collisions is not significant
• New Model
• Beam gas events leave a 1/R2 distribution of
  charge in the TPC
• The charge from the collisions is not significant
  in the 2001 data, but will be in the future (?)

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Uniform .vs. 1/R2 Space Charge Distribution
Distortion
Distortion
Radius
Radius
Z
Z
Radial Distortions
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Two sources of SpaceCharge

• Beam gas and other up stream events
• not synchronous with our trigger
• Scales with beam intensity (not Luminosity)
• 1/R2 distribution of charge (?)
• The collisions at STAR
• synchronous with our trigger
• Scales with Luminosity
• A/R B/R2 distribution of charge (?)
• In the future, the average Luminosity will go up
  a factor of 40 but the beam intensity will only
  go up a factor of 2 to 4
• We have to prepare for a significant increase in
  space charge due to the collisions in the
  detector.

We have to be able to distinguish the two sources
of distortion
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A Wide Range of Charge Distributions
Voltage
Radius
1/R3
1/R2
Wiemans HiJet
1/R
Linear 21
Linear
These (and other) Distributions are Available in
StMagUtilities
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2 Equations, 2 Unknowns

• We can simultaneously fit the DCAs and match the
  steering at the RICH due to the beam gas induced
  space charge
• Choose the right charge distribution 1/R, 1/R2,
  HiJet, etc.
• Choose the RICH scaler normalization constant

with the DCA held constant
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These Items on the List Are Ready to Go

• The list can be enumerated by surfaces
• Outer field cage corrections
• Inner field cage corrections
• Central membrane corrections
• End-wheel and pad-plane corrections
• Pad Row 13 corrections and other local
  electrostatic defects
• Rotation and miss-alignment of sectors with
  respect to their ideal locations
• Rotation of either TPC end-wheel with respect
  to its ideal location
• and by volume
• Space Charge corrections due to charge in the
  volume of the TPC
• Magnetic field corrections due to B fields in
  the volume of the TPC
• Twist of the TPC with respect to the magnetic
  field axis and/or the measured map
• General coordinate transformations
• A few additional items are listed for
  completeness. (And these I dont know about.)

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Conclusions

• Tools are available to calculate all known
  distortions
• in the transverse plane
• gain, t0, and drift velocity corrections have not
  been discussed
• SpaceCharge corrections are significant
• especially at 40x ltLgt
• We need to track the beam current and/or the
  distribution of charge in the TPC for untriggered
  events. We will need scalers and diagnostics for
  each source of charge
• Monitor L
• Monitor beam current
• The RICH Mult Scaler is gone and we need a
  replacement
• Recent progress with the laser cluster finder
  means we might be able to use this data

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DCA, Steering at the RICH, and Dp

• The RICH Scaler has an arbitrary normilization
• The DCAs have been tuned to be the same in both
  cases
• Dp is different by a factor of 2
• Steering at the Rich changes sign under these
  conditions