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The Lead Glass Detector

The Lead Glass Detector. Overview, Experience and Direction. The previous incarnation. An effective mass distribution. 6 photon events identified as hp 0 p 0 Low mass structure is the h” prime Other structures are well known. Use with charged particle measurements.

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The Lead Glass Detector

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  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

  10. 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.

  11. 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 < 500 blocks) • Measure tube responses, relative gains, random noise, data base of tube parameters • $40K, 1 year to complete

  12. Radiation Damage Curing

  13. 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

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