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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 Detector. Reasons for Pixel Detector: Superior signal to noise

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The btev pixel detector and trigger system

The BTeV Pixel Detector and Trigger System

Simon Kwan


P.O. Box 500, Batavia, IL 60510, USA

BEACH2002, June 29, 2002

Vancouver, Canada

Pixel vertex detector
Pixel Vertex Detector

  • Reasons 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

0.25 mm rad-hard FPIX2 chip

  • 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)

The btev pixel detector and trigger system

Comparing to other Pixel Detectors

Luminosity at FermiLab detectors 2x1032cm-2 sec-1

Luminosity at LHC detectors 1x1034cm-2 sec-1

Btev radiation background l 2 10 32 cm 2 s 1 charged hadrons pixels z 55 60 cm
BTeV Radiation Background(L=2·1032 cm-2 s-1), charged hadronsPixels, Z = (55 – 60) cm

Silicon sensor r d v dep vs fluence
Silicon Sensor R&D:Vdep vs Fluence

High density flex circuit development
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

Physics performance of pixel detector
Physics Performance of Pixel Detector

Primary-secondary vertex separation

Minus generated. s = 138m

Distribution in L/s of

Reconstructed Bs

Mean = 44

t proper (reconstructed) - tproper (generated)

s = 46 fs

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 BTeV Level I Vertex Trigger

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!

L1 vertex trigger algorithm
L1 vertex trigger algorithm

  • Generate Level-1 accept if “detached” tracks in the BTeV pixel detector satisfy:



Execute Trigger

Level 2 trigger
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.


  • 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