DØ Central Fiber Tracker
CFT
Description Page
The DØ Central Fiber Tracker (CFT) is part of the DØ upgrade to be installed for operation with the Fermilab Main Injector. DØ was designed with the goals of efficient identification of leptons and jets over a wide rapidity region. This was achieved by using finely segmented, hermetic electromagnetic and hadronic calorimetry, muon detection using thick magnetized iron, and non magnetic inner tracking.
The DØ upgrade extends the capability of the detector to include track momentum determination and vertexing while maintaining angular coverage to eta = +/-3. In addition to the Central Fiber Tracker the upgrade includes:
- A 2 Tesla superconducting solenoid magnet
- A silicon vertex detector
- A preshower detector surrounding the solenoid
- New muon system and calorimeter electronics
- Improvements to the trigger and DAQ systems
The CFT consists of scintillating fibers mounted on eight concentric cylinders. The fibers are double clad and are 835 microns in diameter. The fibers are arranged into ribbons of 256 fibers, composed of two 'singlet' layers of 128 fibers each. These singlet layers are formed into the 'doublet' layers which form the ribbon by placing the fiber centers of one of the singlet layers in the space between the fibers of the other singlet layer. The base-line Central Fiber Tracker design consists of eight doublet layers of scintillating fiber aligned along the beam axis, the axial layers, and four each of U and V stereo fiber layers which make about a 3 degree angle with the axial fibers (constant crossing angle).
The light from the fibers is converted into electrical pulses by visible light photon counters, VLPCs. These are small silicon devices which have an array of eight photo sensitive areas, each 1 mm in diameter on their surface. When operated at temperatures from 6 to 10 degrees Kelvin they have a Q. E. value of over 80% and a gain of 20,000 to 50,000. For more information see; Stefan's and Suyong's page on VLPCs or Stefan's 1994 Como talk.
The detector is divided into 80 sectors in phi. Each wedge shaped sector has 896 fibers and the entire detector has 71,680 channels. The axial fibers, which are 1/2 of the CFT channels, and the axial central preshower channels are used to form a fast level 1 hardware trigger. The axial fibers and the axial and stereo preshower channels are the basis for the subsequent level 2 trigger. All of the fibers are read out on a level 1 trigger accept and are used for a level 3 trigger.
The following half-detector drawing shows the current design for the tracking volume
including silicon Tracker, scintillating fibers, and magnet:
This drawing can be found at -
http://d0server1.fnal.gov/projects/scifi/tracker.GIF
The following drawing shows the cassette assembly courtesy of Eric Haggard:
The drawing (gif) can be found at - http://d0server1.fnal.gov/projects/scifi/assembly.GIF
The following drawing shows the cold end of the cassette assembly courtesy of Eric Haggard:
The drawing (gif) can be found at - http://d0server1.fnal.gov/projects/scifi/coldend.GIF
Last modified August 29, 2005, by SG: stereo angle: changed from '2 degrees with respect to beam axis' to '3 degrees with
respect to axial fibers (constant crossing angle)'; other wording changes.
Please send questions or comments to
Stefan Grünendahl (Stefan@fnal.gov).