The Lead Glass Detector Overview, Experience and Direction

December 2003 The previous incarnation

December 2003 An effective mass distribution 6 photon events identified as     Low mass structure is the  ”  prime Other structures are well known

December 2003 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

December 2003 Correlate with beam If the beam momentum is known, momentum transfer distributions can be measured

December 2003 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.

December 2003 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

December 2003 FCAL can be used in the trigger Deadtimeless digital energy summation on the detector, less than 8  sec Level 3 possible if required, can be very fast, very general requirements can be imposed,

December 2003 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

December 2003 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.

December 2003 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

December 2003 Radiation Damage Curing

December 2003 To do, near term Design/Construction of: Inner frame Cellular Wall Darkroom Cable runs Electronics carriers Monitor system ~$500k, two years, not including electronics

December 2003 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