[d2n-analysis-talk] Dimensions of BigBite Preshower and Shower

[Diana Parno]

> The shower is the most "dimension-sensitive", since it
> provides coordinates that are cross-checked against track.

We also cross-check preshower coordinates against the track. Of  
course, the preshower coordinates along the long edge are not very  
sensitive, since there are only two columns, and the difference is not  
large. But it is worth checking.

> Matt, would you be willing to do this check?  (Or Diana, if you have  
> the
> scripts handy?)

I would be happy to do this but would need a long lead-time -- perhaps  
in another week or two. If Matt can do it sooner, that would be best.

Best,
Diana

On Apr 7, 2011, at 7:15 AM, Brad Sawatzky wrote:

>
> On Wed, 06 Apr 2011, Diana Parno wrote:
>
> [ . . . ]
>> Finally, I looked at our DB files in /usr/local/d2n_analysis/d2n/DB/
>> db_BB.ts.ps.dat and /usr/local/d2n_analysis/d2n/DB/db_BB.ts.sh.dat.  
>> It
>> seems we're using a completely different number there: 35 cm for the
>> long dimension of each block. Here are a few relevant lines from the
>> preshower file:
>>
>> Half of X, half of Y, full Z sizes (in Meters) of Preshower
>>     1.1475  0.35   0.085
>> dx and dy block spacing
>>    -0.085   0.35                                 - Meters
>>
>> And from the shower file:
>>
>> Half of X, half of Y, full Z sizes of Shower
>>    1.1475   0.2975   0.35                        - Meters
>> dx and dy block spacing
>>    -0.085  0.085
>>
>> Recall that X is vertical, so a vertical half-extent of 1.1475 m is
>> consistent with 27 rows of 8.5-cm blocks.
>>
>> So we have here three numbers: the long edge of the blocks could be  
>> 34
>> cm (Transversity), 35 cm (our DB file), or 37 cm (GEn documentation).
>> I wouldn't have expected the calorimeter to be disassembled and
>> reassembled with slightly different blocks so many times in the space
>> of a few years; I suspect there is one right answer, but at this  
>> point
>> I'm not sure how to determine conclusively which one it is. So, I  
>> have
>> two questions:
>>
>> 1. What are the actual dimensions of the BigBite shower and preshower
>> blocks?
>
> Bogdan's the authority, so 8.5 x 8.5 x 34cm it is.
>
>> 2. If they are different from 8.5 x 8.5 x 35 cm^3, then we have the
>> wrong dimensions in our DB file. What effect does that have on our
>> analysis?
>
> It should certainly be corrected, but I wouldn't think it'll make any
> difference.  The shower is the most "dimension-sensitive", since it
> provides coordinates that are cross-checked against track.  The x,y
> dimensions are correct for the shower.  The depth is off by 1 cm, but
> I assume the blocks are positioned inside the full stack relative to
> their upstream face.  If that's the case, then they're just a little
> short -- might matter a little for a Monte Carlo, but it should affect
> the data analysis.
>
> The preshower assembly is 2cm wider that it should be (it'll stretch
> outside the shower solid angle), but I don't think that dimension is
> actually used in a way that would impact the analysis.  It would be a
> small problem if the DB block dimension was too small, since that  
> might
> impact the effective solid angle built in to the shower hit-position
> code.
>
> So, I guess I'm not too worried.  It would be good to replay a run-set
> with and without the updated numbers and then generate a few plots
> for comparison.  The '# particles that pass each cut' would be a good
> set, as would the shower-based position histograms.  Since the same
> files are used in each replay, it is deterministic and statistics  
> won't
> be a big issue (a short replay should be sufficient).
>
> Matt, would you be willing to do this check?  (Or Diana, if you have  
> the
> scripts handy?)
>
> -- Brad
>
> -- 
> 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
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