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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