Pixel%20Readout%20Efficiency - PowerPoint PPT Presentation

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Pixel%20Readout%20Efficiency

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Pixel Readout Efficiency David Christian Fermilab Pixel sensor efficiency Most probable charge deposited 24000 e-. Landau distribution MIP always deposits greater ... – PowerPoint PPT presentation

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Title: Pixel%20Readout%20Efficiency


1
Pixel Readout Efficiency
  • David Christian
  • Fermilab

2
Pixel sensor efficiency
  • Most probable charge deposited ? 24000 e-.
  • Landau distribution ? MIP always deposits greater
    than 14000 e-.
  • Sharing reduces the charge input to an individual
    electronics pixel, but with a discriminator
    threshold of 2000 e-, the detection efficiency is
    gt99.9.
  • The fact that pixels provide space points are
    100 efficient allows BTeV to use very simple
    fast tracking algorithms is the key to the
    success of the experiment.

3
Measured Landau Distribution (p-stop sensor)
Small Amount of Charge loss At corners Should not
be Present in Final sensors.
4
Readout Efficiency Simulation Methodology
  • Generate pixel hits using BTeV Geant
  • Minimum bias at 1E32, 2E32, 4E32, 6E32
  • (Ave. of 1,2,4,6 interactions per crossing
  • includes 1/500 B events w 2x normal
  • track multiplicity 2E32 is nominal rate)
  • Translate file of pixel hits (given for one
    central plane) to list of hit pixels
  • x,y,dx/dz, dy/dz, ( pixels hit) ?
  • list of (row,col,adc)
  • Use Verilog to simulate FPIX2 core (periphery
    assumed not to lose any data)

5
Step 1 BTeV Geant
  • Well tested simulation Monte Carlo.
  • Used (for proposal) to simulate detector response
    to a variety of B decays of interest will be
    maintained for use throughout the life of the
    BTeV experiment.
  • Includes a pretty good guess of all material in
    the active area.
  • Charged particles are propagated through magnetic
    field allowed to scatter, interact, radiate
    photons in material.
  • Neutrals propagated allowed to scatter,
    interact, and (photons) pair produce ee-.
  • Simulation includes d-rays with energy gt 1 MeV

6
Step 2 Generate list of hit pixels
  • FORTRAN program allows one to select an arbitrary
    chip position with respect to the beam hole.
  • Uses track slope in x y to figure out which
    pixels are traversed (includes sharing across
    columns as well as across rows).
  • Adds a small dx dy to account for charge
    diffusion.
  • Calculates ADC using track length in cell (simply
    proportional to length no Landau).

7
Step 3 Verilog Simulation
  • Very simple model of sensor/FPIX front end
  • Two parameters are set depending on (input) 5-bit
    pulse ht
  • Discriminator timewalk (with respect to BCO)
  • Analog memory (time that no 2nd hit is allowed)
  • Complete and accurate model of digital aspects of
    FPIX core.
  • Models 160 rows x 18 columns
  • Max. readout clock frequency determined by
  • Horizontal vertical token passing
  • With 160 rows, vertical token limits clock to ?
    30 ns
  • Almost all data loss occurs because EOC timestamp
    registers fill up. Minor EOC logic error
    identified.

8
Representative (preliminary)Verilog Results
interactions per crossing R/O Eff. with 30 ns clock R/O Eff. with 25 ns clock
1 99.8
2 99.7
4 99.1 99.3
6 96.4 98.2
9
Known deficiencies
  • Geant ignores d-rays below 1 MeV
  • (can be added in step 2).
  • Geant include no accelerator backgrounds, such
    as tracks from beam-gas interactions or muons
    from scraping on magnets, etc.
  • FORTRAN program (step 2) doesnt include magnetic
    field effect (increases sharing across columns in
    non-bend view by 12.5 changes sharing along
    rows in the other view).
  • FORTRAN program doesnt yet include d-rays.
  • Procedure underestimates multiplicity slightly
  • (15-50)?

10
Trigger sensitivity to pixel inefficiency
Trigger loses efficiency quickly as pixel
efficiency degrades
Inner chip Efficiency Efficiency of Balance Trigger Efficiency for Bs ? DsK
100 100 74
99.5 99.5 72
99 99.5 71
97.5 99 99.5 68
Almost a 10 loss
11
What efficiency is achievable?
  • Sources of loss
  • Missing bump bonds
  • Hot pixels
  • Data loss in FPIX2
  • Missing bumps
  • Experience so far ? 0.1 is achievable
  • (although most of the sensors we have tested so
    far have regions containing no bumps amounting to
    gtgt 0.1)
  • Hot pixels
  • Very little experience (limited statistics)
  • (1-2)/1300 in each FPIX1 sensor pixels
    connected to two electronics pixels (1-2)/700
    ? 0.3
  • Conclusion Missing bumps Hot pixels ? 0.5

12
Readout efficiency requirement (proposed)
Luminosity Inner chip efficiency Efficiency of balance Trigger Efficiency for Bs ? DsK
Nominal (2 x 1032) gt99.5 gt99.9 71
2 x Nominal (4 x 1032) gt99 gt99.8 70
3 x Nominal (6 x 1032) gt98 gt99.5 68
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