BTeV Beam Test Results

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VERTEX 2000 Sep 10 - 15 , 2000 Homestead,
Michigan
BTeV Beam Test Results
Jianchun Wang Syracuse University Representing
J.A. Appel, J.N. Butler, G. Cardoso, H. Cheung,
G. Chiodini, D.C. Christian, E.E. Gottschalk,
B.K. Hall, J. Hoff, P. A. Kasper, R. Kutschke,
S.W.Kwan, A. Mekkaoui, R. Yarema, and S.
Zimmermann Fermi National Accelerator
Laboratory C. Newsom - University of Iowa A.
Colautti, D. Menasce, and S. Sala - INFN(Milan)
R. Coluccia and M. Di Corato - Universita di
Milano M.Artuso and J.C. Wang Syracuse
University
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The BTeV Detector
Pixel Vertex Detector Dipole Magnet Magnet
Coil Beam Pipe
Forward tracking RICH PbWO4 EM calorimeter Muon
Toroid
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The BTeV Pixel Detector

• Function
• Deliver clean, precise space points to detached
  vertex trigger
• Provide vertex information for offline analysis
• Pixel sensor
• Eliminate ambiguity problems with high track
  density (essential to the detached vertex
  trigger)
• Radiation hard, low noise
• Easy pattern recognition
• Pixels size 50mm ? 400 mm (total 3 ? 107
  channels)

31 2-plane pixel stations
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Goals of Beam Test

• Gain operational experience, look for potential
  problems and sensitivities
• Study the spatial resolution dependence on track
  incident angle, digitization accuracy, bias
  voltage and threshold
• Determine validity of our sensor simulations
• Compare different detector technologies
  (p-stop, p-spray)

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Beam Test Telescope
SSD
SPD
SSD

• Beam 227 GeV p
• Tracking 6 plane SSD in two boxes
• SPD box provides different incident angle 0, 5,
  10, 15, 20, 30 degree
• 4 SPD tested with ATLAS sensor prototypes

? 227 GeV
X-Y-X
X-Y-X
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Silicon Pixel Detector

• Readout Chip
• FPIX0 64?12 cells, 8-bit external ADC
• FPIX1 160?18 cells, 2-bit internal FADC

• Pixel sensor (nnp)
• ST1-CiS p-stop (FPIX0)
• ST2-CiS p-spray (FPIX0)
• ST1-Seiko p-stop (FPIX1)
• ST2-Seiko p-spray (FPIX1)

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Front End Electronics
See David Christians talk

• FPIX0 analog output, with external 8-bit ADC
• FPIX1 digital output, with internal 2-bit FADC

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Pulser Calibration

• FPIX0 bump-bonded to ST1 CiS p-stop sensor
• Threshold 2500 e Noise 106 e
• External ADC introduce noise Total 400 e

Qnoise,ADC40096e- Dynamics 1.5MIP
Qth2500400e- Qnoise10613e-
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X-ray Source Calibration

• Absolute Calibration
• Discriminator threshold
• Amplifier noise
• ADC scale

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Charge Collection
Peak 24.7 ke FWHM 10 ke
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Charge Collection
FPIX0 p-spray
Qmp 18300 e
Charge loss not intrinsic to the p-spray
technology, but a feature of this particular
sensor punch-through biasing, and floating
atoll
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MC Simulation
The interplay of these factors has been studied
with a Monte Carlo simulation including

• Energy deposition by charged track along its path
  length (spread of the electron cloud due to
  diffusion)
• Drift in E corresponding to doping and bias
  voltage applied
• E ? B (our sensors will be in dipole field of 1.6
  T)
• Realistic parameters of the front end electronics
  (noise,threshold, digitization accuracy)

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Charge Sharing
Relative Fraction of Cluster Size
FPIX0 CiS p-stop Qth 2500 e- Vbias
-140V Vbias -85V
Delta ray emission results in larger cluster size
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Position Reconstruction

• Error of predicted track position 2mm -
  2.5mm, Not subtracted from measured resolution
• Charge weighting and s-curve correction used for
  clusters with 2 or more pixels

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Charge Sharing

• Non-Gaussian residual distribution for 1-pixel
  cluster
• Resolution fit needs to consider the special
  shape
• For small incident angle tracks, the fraction of
  1-pixel clusters is proportional to spatial
  resolution

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Resolution vs angle

• No track projection error subtracted from the
  measurement
• Resolution distribution agrees with simulation
• Binary resolution degraded from 8-bit ADC

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Resolution Oscillation
Simulation
Resolution oscillation in binary mode due to
change of dominant cluster size
Binary Readout
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Comparison of Different Detector

• Most of difference due to the different readout
  thresholds
• The charge losses in FPIX0 p-spray degrades the
  spatial resolution
• BTeV requirement better than 9 mm

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Digitization Accuracy
FPIX0 p-stop

• 2 bit ADC is degraded from 8-bit ADC
• Resolution of 2-bit ADC is slightly worse than
  8-bit
• FPIX2 will use 3-bit FADC

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Resolution vs Bias Voltage

• For 0 track, lower Vbias ? more diffusion
• ? less fraction of Npixel1 ? better resolution

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Resolution vs Threshold
FPIX0 p-stop
Large readout threshold degrades the spatial
resolution
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Occupancy Test

• 2.2 mm thick diamond target used
• Handle occupancy much larger than expected at
  BTeV ( factor of 10 )

Interaction vertex in diamond target
Interaction vertex in pixel plane
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Summary

• Large data sample to gain operational experience
  with pixel silicon detectors ( 3M events)
• The FPIX type front end electronics performs well
• Resolution has little sensitivity to the bias
  voltage, but sensitive to readout threshold
• Good resolution at all angles, meets 9mm
  requirement, and 3-bit ADC is a good choice for
  FPIX2
• Excellent tracking capability, can easily handle
  the BTeV multiplicity by 50mm?400mm pixels
• Monte Carlo simulation describe well the real
  feature

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Charge Sharing
Relative Fraction of Cluster (row) Size
FPIX0 CiS p-stop Qth 2500 e- Vbias
-140V Vbias -85V
Delta ray emission results in larger cluster size
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Charge Sharing
Relative Fraction of Cluster (row) Size
FPIX1 Seiko p-stop Qth 3780 e- Vbias
-75V Vbias -45V
Delta ray emission results in larger cluster size