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

[Diana Parno]

I'm resolving corrections to my thesis and realized that there seem to  
be some ambiguities about the geometry of the BigBite shower and  
preshower blocks. I am hoping somebody here (Brad, maybe?) knows what  
the actual geometry is.

In the Transversity dissertations, e.g. page 165 of Xin's thesis or  
page 74 of Kalyan's thesis, the size of the preshower and shower  
blocks is given as 8.5 cm x 8.5 cm x 34 cm (of course, the orientation  
is different in the two layers). However, they both also state the  
active area of the preshower as 210 x 74 cm^2, and the active area of  
the shower as 221 x 85 cm^2. This does not add up. If you go by the  
height of a block times 27 rows, the vertical active length should be  
229.5 cm. Applying the same arithmetic to the horizontal dimension,  
the 7 columns x 8.5 cm/block gives a horizontal active length of only  
59.5 cm (not 85) for the shower, and 68 cm (not 74) for the preshower.  
These reports from Transversity are not internally consistent. (You  
could reduce the active area by giving the calorimeter less than 100%  
acceptance, or if you were taking into account the pitch angle and  
taking a projection of the area onto a plane exactly perpendicular to  
the floor, but you can't increase it that way.)

I found a report about the calorimeter setup, prepared by Sergey  
Abrahamyan for GEn, here: http://hallaweb.jlab.org/experiment/transversity/bigbite/bigbite_gen.ps 
  . This gives block dimensions of 8.5 cm x 8.5 cm x 37 cm, which  
would explain where the "74 cm" number for the preshower layer's  
horizontal extent came from. The figure is also internally consistent,  
i.e. the total vertical and horizontal dimensions of the layers agree  
with the reported sizes of the blocks.

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?
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?

Best,
Diana