The BTeV Pixel Detector and Trigger System
Simon Kwan
Fermilab
P.O. Box 500, Batavia, IL 60510, USA
BEACH2002, June 29, 2002
Vancouver, Canada
The BTeV Spectrometer
Pixel Vertex DetectorReasons for Pixel Detector:•Superior signal to noise•Excellent spatial resolution -- 5-10 microns depending on angle, etc•Very Low occupancy•Very fast •Radiation hard
Special features:•It is used directly in the Level 1 trigger•Pulse height is measured on every channel with a 3 bit FADC•It is inside a dipole and gives a crude standalone momentum
Hybrid Silicon pixel devices
• Independent development and optimizations of readout chip and sensor
• n+ pixels on n-type substrates: inter-pixel insulation technology under investigation
• Bump-bonding of flipped chip: 2 technologies being considered: Indium (In) and solder (SnPb)
0.25 m rad-hard FPIX2 chip
Comparing to other Pixel Detectors
Experiment
Property
ALICE
Pb-Pb
Collider
ATLAS
p-p
Collider
CMS
p-p
Collider
BTeV
p-pbar
Collider
Pixel Size
50 x 425
50 x 400
150 x 150
50 x 400
Min. distance
to beam
40 mm 43 mm (B)
101 mm
41 mm
70 mm
6 mm
Number of
Pixels
16 x 106 140 x 106 56 x 106 22 x 106
Total Active
Area
0.26 m2 2.2 m2 1.1 m2
0.60 m2
Material Xo
per plane
1.4 % 1.80 %
1.62 %
1.65 %
2.3 %
1.2%
Special Features 50 tracks/cm2 4 bit TOT
ADC
Low luminosity
inner layer
Level 1 Trig
3 bit ADC
Luminosity at FermiLab detectors 2x1032 cm-2 sec-1
Luminosity at LHC detectors 1x1034 cm-2 sec-1
BTeV Radiation Background(L=2·1032 cm-2 s-1), charged hadrons
Pixels, Z = (55 – 60) cm
Pixel Readout Chip
FPIX2
•Reat out rate: 132 ns crossing time
•Greater output bandwidth to easily readout all hit data and provide to trigger
•R&D started in 1997
•Two generations of prototype chips(FPIX0 & FPIX1) have been designed& tested, with & without sensors,including a beam test (1999) inwhich resolution <9was demonstrated.
•New “deep submicron” radiationhard design (FPIX2):Three test chipdesigns have been produced & tested.(radiation hardness tested, no changeafter 2x 1015proton/cm2)Each with increasing complexity.
A pixel
Test outputs
Readout
Irradiation Results: Pixel ROC
Silicon Sensor R&D:Vdep vs Fluence
High density flex circuit development
•15 HDI delivered from CERN; only 4 without defects•Preliminary performance assessment very satisfactory design validation•We need to do more extensive tests and find commercial vendor for large scale production
Built 10% Model
The Pixel Detector (2-D Side View)
Physics Performance of Pixel DetectorDistribution in L/ of Reconstructed Bs
Primary-secondary vertex separationMinus generated. = 138
proper (reconstructed) - proper (generated)= 46 fs
Mean = 44
The BTeV Level I Vertex Trigger
• Key Points– This is made possible by a vertex detector with
excellent spatial resolution, fast readout, low occupancy, and 3-d space points.
– A heavily pipelined and parallel processing architecture using inexpensive processing nodes optimized for specific tasks ~ 3000 processors (DSPs).
– Sufficient memory (~1 Terabyte) to buffer the event data while calculations are carried out.
The trigger will reconstruct every beam crossing and look for TOPOLOGICAL evidence of a B decaying downstream of the primary vertex. Runs at 7.6 MHz!
• Generate Level-1 accept if “detached” tracks in the BTeV pixel detector satisfy:
2
2.0
25.02
b
mb
pT
(GeV/c)2
cm
L1 vertex trigger algorithmExecute Trigger
b
p p
B-meson
L1 trigger efficiencies
Process Eff. (%) Monte Carlo
Minimum bias 1 BTeVGeant
Bs D+sK- 74 BTeVGeant
B0 D*+- 64 BTeVGeant
B0 00 56 BTeVGeant
B0 J/s 50 BTeVGeant
Bs J/*0 68 MCFast
B- D0- 70 MCFast
B- Ks- 27 MCFast
B0 2-body modes 63 MCFast
()
Level 2 Trigger
• Start with the Level 1 tracks from the ``triggering collision” within the crossing.
• Search for pixel hits along these tracks.
• Refit the tracks using a Kalman Filter. Resultant momenta are improved to about 5-10%.
• Resultant event must satisfy one of the two following criteria:
– A secondary vertex must be present or
– The collection of tracks must satisfy a minimum pT cut.
• The combined L1 and L2 rejection is 1000-1.
• Overall Efficiency is roughly 50% for most B decays of interest.
Summary
• Great progress has been achieved in the design of the sensor, front end electronics and module structure of the BTeV pixel detector
• We are making rapid progress towards a full system design that satisfies all the BTeV requirements
• This vertex system will be the key element of the Trigger algorithm that will enable efficient collection of a variety of beauty decays & provide a superb tool to challenge the Standard Model