[d2n-analysis-talk] BB H2 elastic shower

[posik at jlab.org]

Hi Brad,

   In our last meeting you had told me to look into the odd shower energy
plots. The BB.ts.ps.e/2+BB.ts.sh.e (y-axis total calorimeter energy) vs
BB.ts.ps.e (x-axis preshower). What I noticed is that in transversity
they had the preshower position defined by this line in the
db_ts.ps.dat file

X,Y,Z coords (in cm) of Preshower front plane in spectrom cs
                        -0.015     0.0    0.97           - Meters

And in our DB we have the line

X,Y,Z coords (in cm) of Preshower front plane in spectrom cs
                         0.0     0.0    0.77           - Meters

So I did a replay with the preshower positions from transversity and below
is the comparison between the two.(before_e.png is using our current DB
files, after_e.png is using the transversity preshower positions). In both
plots the following cuts were applied:

   T5 (coin trigger cut) + (BB.tr.n==1) + neg charge particle.

With the transversity preshower positions a lot of those particles
appearing in the low preshower in the before plot seem to move to higher
preshower channels, meaning that they were good electrons. This supports
what I seen when I cut on the low preshower particles in the before plot
and looked at the cherenkov TDCs and seen that some of the TDCs had a
clear sharp signal, which would not indicate pions.

I think that our preshower location in the DB is wrong. However, I would
like to be sure of this and find the position my self. So the first place
I looked is here:

http://hallaweb.jlab.org/experiment/transversity/wikifile/Big_Bite_Spectrometer_Sect_Oct29-annot.pdf

Which shows a schematic of BigBite in the Hall A coord. system. But I also
have the survey report, which I think maybe more accurate, found here:

http://www.jlab.org/accel/survalign/documents/dthalla/A1219.pdf

I was wondering if there is a key or something that tells you what the
1CL, 1TOPBR , ect are ?

Thanks
Matt
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