Re: FCAL test

[David Lawrence <davidl@jlab.org>]

Matthew Shepherd wrote:
>
> On Sep 16, 2007, at 9:55 PM, David Lawrence wrote:
>
>> This problem can be overcome by breaking your "outer" detectors into 
>> 4 groups and shifting them like an iris so that they exactly bound 
>> the "inner" detectors.
>
> Aha yes, .. interesting -- although with the circular stack of glass 
> that will add a whole new degree of difficulty to the glass support 
> structure.

Engineers love a challenge.
>
>> PrimEx also did beam tests to study the boundary between lead glass 
>> (TF-1) and lead tungstate (PbWO4). The lead glass was 3.84x3.84 cm^2 
>> while the PbWO4 was 2x2 cm^2. I can't seem to find the note just now, 
>> but I can dig it up if you are interested.
>
> I remember talking to you about this at one point.  Didn't you say 
> that even after extensive beam tests most PrimEx analyses tossed out 
> these "hybrid" showers that hit the overlap region?
>

It wasn't so much the boundary as the entire outer, lead glass part of 
the calorimeter. The lead glass had much poorer resolution than the 
PbWO4 and all of our physics signal was in the PbWO4. The main benefit 
of the lead glass was to increase the range of our angular acceptance so 
that we could fit the background better that extended under our signal. 
Because of the poor resolution, including the lead glass in the analysis 
increased part of our systematic error.

Regards,
-David

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