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A proposal for setting a BCAL threshold




Hi All,

Here's a proposal for setting a BCAL threshold so we can start to  
refine the reconstruction a little bit.

- take dark rate at 32 MHz (design goal from GlueX-doc-795) and  
assume this is only single PE rate
- for a 100 ns window this means an average of 3.2 pulses per window
- assume the fADC processing just generates a pedestal subtracted  
mean and that dark rate (not electronics noise) dominates the pedestal
- let's assume the DAQ can handle 5% occupancy in the BCAL
- if average is 3.2 dark pulses, the probability of having 7 or more  
pulses in a window is 0.04

--->> set threshold at 7 photoelectrons

7 photoelectrons * ( 26 keV_fiber / pe ) / 12% = 1.5 MeV energy  
deposited in cell

I propose we adjust the threshold to 1.5 MeV (down from 10 MeV) and  
work from there.  Of course this needs further study, and validation  
through whatever bench studies, beam test, etc. etc..  My main goal  
is to get around the right order of magnitude so we can make another  
pass at the reconstruction algorithm which will behave very  
differently with this much lower threshold.  Does anyone see a  
serious flaw with this?

-Matt