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Re: A proposal for setting a BCAL threshold



Matt,

The design goal of 32MHz may eventually be achieved, but this is not 
demonstrated.  At the last meeting George agreed that 100MHz is 
achievable with what he has seen.  I would believe something more like 
150MHz @ 22C from what I have actually seen, but I am not working with 
Sensl modules.  This depends a lot on temperature, but we agreed that we 
do not want to have to refrigerate the BCal readout very much.

Richard J.

Matthew Shepherd wrote:
>
> 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
>

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