The Lead Glass Detector

1
The Lead Glass Detector

• Overview, Experience and Direction

2
The previous incarnation
3
An effective mass distribution

• 6 photon events identified as hp0p0
• Low mass structure is the h prime
• Other structures are well known

4
Use with charged particle measurements

• The FCAL can reconstruct a decay into all
  photons, the resulting reconstructed particles
  can be used with charged particle measurements

5
Correlate with beam

• If the beam momentum is known, momentum transfer
  distributions can be measured

6
Time measurements

• At right is a typical pulse from a PMT, digitized
  at 2GHz, 8 bits. Marked are location of the pulse
  peak and 50 crossing. A library of such pulses
  exists.

7
Time measurements

• Scope sampled pulses fitted to polynomial to
  extract feature times
• Compressed to simulate 8 bit/250 MHz signal
• Algorithm used to determine feature time
• 300 ps resolution is possible
• Each block in a photon cluster gives a time
  measurement
• Time measurements are independent of vertex
  position and momentum

8
FCAL can be used in the trigger

• Deadtimeless digital energy summation on the
  detector, less than 8 msec
• Level 3 possible if required, can be very fast,
  very general requirements can be imposed,

9
Current status

• All blocks, tubes at Jlab, Inner frame at IU
• Status of tubes unknown, were working in 1997
• Status of glass unknown, some radiation damage
  observed in 1995, very localized, caused by
  mis-steered beam. Some blocks used in RadPhi,
  known to be damaged
• No appropriate mechanical structures exist

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Current status, contd.

• Design of digitizer has begun, Paul Smith
  will/has say/said more
• Magnetic field/shielding studies begun, have
  shown cellular wall shields longitudinal field,
  shielding effect increases as distance from an
  edge. Inner frame material an issue.

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To do, short term

• Transfer glass, tubes to IU for evaluation
• Measure transmission of blocks, data base to
  determine block quality, UV cure any damaged
  blocks (probably lt 500 blocks)
• Measure tube responses, relative gains, random
  noise, data base of tube parameters
• 40K, 1 year to complete

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Radiation Damage Curing
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To do, near term

• Design/Construction of
• Inner frame
• Cellular Wall
• Darkroom
• Cable runs
• Electronics carriers
• Monitor system
• 500k, two years, not including electronics

14
To do, longer term

• Outer frame appropriate for specific application,
  for example, GlueX
• Motion along beam, small motion transverse to
  beam for alignment
• Interfaces to services, DAQ, power,
  cooling/heating, fire suppression, safety, etc.
• Integration with other detector elements, ToF in
  particular
• Budget undetermined/Construction issue