The Scintillating Fiber Tracker and Muon Trigger at DZero

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The Scintillating Fiber Tracker and Muon Trigger
at DZero

• Maris Abolins
• For the D0 Collaboration

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Upgraded D0 Detector
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The DØ Scintillating Fiber Tracker

• 8 nested cylinders
• r 20 51 cm
• On each cylinder scintillating fibers
• 2.5m or 1.7 m, long
• 835 um diameter
• Fibers arranged into
• 1 axial doublet
• 1 stereo (u or v)
• Constant pitch 3o
• Total channel count gt77K
• Clear fiber, 7 - 11m long, brings signal to VLPCs

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DØ Scintillating Fiber Tracker Operational
Principles
Optical Connector
Scintillating Fiber
Mirror

• A charged particle crosses a scintillating fiber,
  where it causes a blink of light.
• The light is transported via optical fiber over a
  distance of 8-11 meters to a device called a VLPC
  which converts light into electricity.
• VLPC is a solid state device that operates at
  cryogenic temperatures.
• A cassette of VLPC devices contains 1024
  channels and is housed in a cryostat, which
  carefully regulates the operating temperature.

Waveguide Fiber
Electrical Signal Out
Photodetector Cassette
Cryostat
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DØ Fiber Tracker
Eight cylinders covered with scintillating
fiber are read out with a novel light
detector (VLPCs).
VLPCs
See the Display!
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VLPC History

• In 1987, a paper was published by Rockwell
  detailing the performance of Solid State
  PhotoMultipliers (SSPMs). These solid state
  devices detected both visible and infrared light.
  Infrared detection technology is regulated under
  international treaty so Fermilab proposed a
  device which maintained the visible light
  response, but reduced the infrared response.
  This device is called a Visible Light Photon
  Counter (VLPC).
• With the successful demonstration of VLPC
  technology, the High-Resolution Scintillating
  Fiber Tracking Experiment (HiSTE) proposal
  detailed using scintillating fiber technology
  combined with VLPCs to track particles from high
  energy particle collisions. There have been six
  models of HiSTE chips, with HiSTE-VI being used
  in the DØ experiment.

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VLPC Operational Principles

• Photon is converted in the intrinsic region,
  creating an electron-hole pair.
• Hole drifts into the drift region, where it
  knocks an electron out from an atom.
• Electron accelerates back through gain region,
  knocking electrons from atoms as it goes.
• Spacer region and substrate are for mechanical
  support and field shaping.
• Thus each photon generates a pulse of many
  electrons. Gains of 20,000 60,000 are
  achievable.

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HiSTE VI

• Solid state photon detectors
• Operate at a few degrees Kelvin ( -450 F)
• Bias voltage 6-8 Volts
• Detect single photons
• Can work in a high rate environment
• Quantum efficiency for visible light 80
• High gain 50 000 electrons per converted photon
• Low gain dispersion
• Highly suppressed infrared sensitivity

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2
0
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Visible
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HISTE VI
Wafer
VLPC Chip
0.30 cm (0.12)
7.62 cm (3)
Each VLPC pixel is a 1 mm diameter detector, well
suited for use in scintillating fiber
applications.
Each wafer is grown via vapor phase epitaxy
and then masked for the desired configuration.
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Gain

• Gains (in thousands)
• Range from
• 20 000 to 60 000
• Gain dispersion of the pixels within one chip
• About 1.5

20 000
60 000
1.5
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Quantum Efficiency and GainBehavior

• QE and gain are a function of voltage
• Relative gain is highly correlated

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Linearity at 0 MHz Background
Normalization Point
Gain 30 000
Measurement Artifact
Gain 50 000

• VLPCs are linear to lt10 for Equivalent PE 600
  (750 photons).
• Increasing non-linearity with increasing gain.

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Connected Fibers - Stereo Board Only
Lack of final electronics has forced us to
read out a portion of the CFT with
prototype electronics
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Event Displays (magnet off)
Instrumented Region
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Fiber Occupancy (Min Bias)
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Summary

• Tracking hardware installed and working
• Electronics
• 25 on hand now
• The remainder scheduled to arrive within 1month
• Will need another 1 month for installation and
  checkout

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DØ Muon System
Muons provide a signature of many interesting
physics events. Muons penetrate dense material
for long distances. Thus muon detectors are
outside the large amount of metal that makes the
rest of the detector. The muon system consists of
many different detector technologies, and is the
physically largest system.
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Muon scintillators
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Muon drift tubes
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Mu Trigger schematic
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Muon front ends
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SLIC
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SLIC Outputs
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Alpha outputs
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Software Projects
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L1MU Status

• Work in progress
• Developing L1MU examine - highest priority
• Tracking down Muon FE - L1MU interface problems
• Understanding muon octant trigger rates
• Verifying that the Muon FE systems are timed in
  to the correct BC
• Understanding and fixing a number of hardware
  bugs
• Completing software connection to COOR
• Increasing sophistication of triggers
• Continuing development of trigger simulation

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L1MU Trigger Rates _at_ 4e30
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Summary

• Much of detector hardware installed and working
• Most trigger electronics installed and undergoing
  tests
• Most of software elements are in place
• Monitoring software is a high priority