[d2n-analysis-talk] BB Cerenkov hardware threshold

[Brad Sawatzky]

The online discriminator threshold was 70mV as you found (it's also at
the end of every start-of-run halog entry).  That is roughly 1.5 p.e.'s
This is is the signal that helped form our primary trigger.

The optimal offline threshold is the one that Matt's study identified as
giving the optimal signal:noise ratio.

We would have run with a 3 p.e. threshold in the online trigger if the
mirrors had been good enough to give us the predicted number of photons
per electron track.  This would have made a huge difference in the
performance of the Cerenkov on the beamline-side.  Unfortunately the
mirrors turned out to suck, and we had to run with a lower threshold.

-- Brad

On Mon, 07 Feb 2011, Diana Parno wrote:

> I'm wondering what the hardware threshold on the BB Cerenkov was  
> during the experiment, in terms of number of photoelectrons. I found a  
> HALOG entry placing the threshold at -0.070 V:
> 
> http://www.jlab.org/~adaq/halog/html/0902_archive/090210201819.html
> 
> Brad's Cerenkov tech note talks about gain-matching the PMTs to place  
> the one-p.e. peak at about 50 mV, which would put the threshold at  
> about 1.4 p.e. On the other hand, page 4 talks about a 3-p.e.  
> threshold, and I am not sure from context whether that's supposed to  
> be a hardware (online trigger) threshold or a software (offline cut)  
> threshold. If the threshold is 1.4 p.e., do we have a rough idea as to  
> the online pion rejection factor? (If it's 3 p.e., then Matt's study  
> from last month would give that factor, if I'm not mistaken.)
> 
> Best,
> Diana
> 
-- 
Brad Sawatzky, PhD <brads at jlab.org>  -<>-  Jefferson Lab / Hall C / C111
Ph: 757-269-5947  -<>-  Fax: 757-269-5235  -<>- Pager: brads-page at jlab.org
The most exciting phrase to hear in science, the one that heralds new
  discoveries, is not "Eureka!" but "That's funny..."   -- Isaac Asimov