Title: Pixel%20Readout%20Efficiency
1Pixel Readout Efficiency
2Pixel 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.
3Measured Landau Distribution (p-stop sensor)
Small Amount of Charge loss At corners Should not
be Present in Final sensors.
4Readout 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)
5Step 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
6Step 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).
7Step 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.
8Representative (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
9Known 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)?
10Trigger 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
11What 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
12Readout 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