[d2n-analysis-talk] BB shower calibration

[posik at jlab.org]

Hi all,

  So I have been looking at the BigBite shower. I did a 4-pass calibration
on it using runs from 2056-2086. After I had gotten the coefficients by
minimizing the energy:

  E = c*A, where E is the scattering energy, c is the coefficient and A is
the ped subtracted ADC of the shower block.

I then replayed run 2060 with the new coefficients (see plot T2_2060.png).
The top left shows 2 times preshower energy in MeV, the top right shows
the shower energy in MeV, the middle left shows the total
shower+0.5*preshower energy in MeV (red histo) and the momentum in MeV
(blue histo), the middle right shows the E/p, the bottom left shows the
dE/E ( shower_energy+0.5*preshower_energy- momentum)/momentum and the
bottom right shows the E/p (y-axis) vs the preshower (2*MeV, x-axis).

 When I saw this it was rather odd that the total shower energy and the
momentum did not seem to agree (middle left plot), they differed by ~7%.
I do not really know why the momentum and the energy would not line up,
could it be the discontinuity in the momentum?

What I did next was increased the coefficients by 7% and produced the same
plots (see T2_7_2060.png). Now the total shower and preshower seem to
align better as well as the E/p. I had thought that maybe since I took a
spread of 4-pass runs to do the calibration and was looking at only one
run here, that maybe the total shower energy and momentum didn't align
just because of a fluctuation of the E/p peak from run to run. So I
checked a couple of the other runs used in the calibration, 2073,2080 and
they give the same results as run 2060. The three runs give a resolution
consistent with dE/E and E/p of ~9%.

I then decided that maybe I could apply the shower coefficients to a H2
elastic run 1258, and see where the total energy peak falls relative to
the momentum peak. So doing this I was able to produce the plots found in
1pass_sh.png. The plot layouts are the same as the previous ones.

 The thing that I noticed about the total energy(red histo) and the
momentum(blue histo) (middle left plot), is that their peaks seem to
agree with a mean of ~890 MeV, which is the expected scattering energy at
45 degrees. The total energy has a wider spread than the momentum, but
that would be expected since the shower energy is constructed for the
shower blocks that have a significant width to them so the resolution
will not be as narrow as the momentum,although the E/p and dE/E
resolution seems to be a bit worse than what I seen at 4-pass. The dE/E
resolution here is ~10%.

 I am now looking at runs 2060,2073 and 2080 together with Cerenkov cuts
applied, but I am not really sure where to head from here.


Thanks
Matt
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