Re: Geometries for 2008 DC Review

[David Lawrence <davidl@jlab.org>]

Hi Matt,

    Thanks for those plots. Just to clarify though, my comment was aimed 
at the *relative* difference in the "summer 2007" and the "winter 2007" 
efficiency plots compared to the *relative* difference in the radiation 
length scans. If I look at the black markers on Mihajlo's plot for 
angles greater than 13 degrees, there are 2 very clear flat areas with 
valleys in between. The valleys, I assume, are due to the frames and 
their depths are correlated with the amount of material in the frames. 
If I look at the radiation length scans, I can see the peaks for the new 
geometry are about 1/3 to 1/4 as high as for the old geometry. This 
makes me think I should see valleys that are 1/3 to 1/4 as deep in the 
red markers as in the black. Granted, these may be small, but if I focus 
only on the black markers in Mihajlo's plot and visual valleys that are 
1/3 shallower, I think I should still see them easily.

Your plots are interesting since if I look at the pair on the right 
(0-120 degree range), I think I can see the structure maps from the top 
to the bottom. For the pair on the left though, the bottom plot looks 
more like statistical fluctuations than any real reflection of the 
structure. It would be interesting to see that plot with a lot more 
statistics.

Regards,
-David

Matthew Shepherd wrote:
>
> Hi Mihajlo and Dave,
>
> On Jan 24, 2008, at 12:06 PM, David Lawrence wrote:
>
>> I do see the positions and heights of the peaks have changed quite a 
>> bit. But, not so much so that I expect to see as flat of a 
>> distribution as I see in your plots. I could be wrong though, but I'm 
>> hoping when you re-run with the exact geometries I'm using, we sill 
>> consistent pictures.
>
> I suggest Mihajlo generate plots of both conversion probability and 
> efficiency to provide a definitive answer since I suspect the 
> confusion is in the distinction between these two.  Attached are 
> similar plots for only the current geometry.  Conversion probability 
> is directly related to David's radiation length scans, but efficiency 
> is not necessarily since converted photons can be reconstructed if 
> secondary particles still form a nice cluster.  You can get an idea of 
> the magnitude of this effect by comparing the attached plots.  In the 
> ring region the efficiency is up around 85-90% but the conversion 
> probably is still in the 20-30% range.
>
> -Matt

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