[d2n-analysis-talk] preshower block dimension change results

[posik at jlab.org]

Hi all,

  So after Diana found that our data base is using the wrong y dimension
for the preshower blocks, (we have 35cm and they are really 34cm), I
went and checked what affect there would be by using 34cm rather than
35cm. I did this by replaying 4-pass 3He runs 2065 and 2068 using a
block y size of 35cm and then again but with a block size of 34cm.

You can find the plots that I used here:

http://jlab.org/~posik/d2n/BB/ps_dim_test_plots/

There are two subscripts, "with" and "without", in each saved plot. The
with subscript has the BigBite Preshower y block size set to 34cm and the
without is set to 35cm.

For all plots I used the following cuts:

TCut cut =
"((DBB.evtypebits&1<<2)==(1<<2))&&(TMath::Abs(BB.tr.vz[])<0.17)&&(BB.optics.charge[]==-1)&&(BB.optics.vzflag[]==1)&&(BB.tr.p[]>0.0)";

Below I describe what the plots are showing. There were 3 canvases drawn
c1,c2,c3 for both the "with" and "without" block change.

Going from top left, top right, bottom left and bottom right in each
canvas we have:

c1:
  shows the reconstructed tracks, pre-shower energy, shower energy and
momentum

c2:
  Pre-shower X, pre-shower Y, preshower x - BB.tr.x - 0.97*BB.tr.th,
preshower y - BB.tr.y - 0.97*BB.tr.ph

c3:
  preshower energy vs shower energy (MeV) (left plot), Total BB energy vs
momentum (MeV) (right plot)


Results:
===========

All plots that I looked at (see above) were identical except for the
difference of the preshower Y - projected Y track. This has a difference
in the mean of -6.7mm. This should not affect anything. Our Cut on
preshower Y - Proj. track y is

pspos =
Form("((TMath::Abs((BB.tr.x[]+0.97*BB.tr.th[])-(BB.ts.ps.x+%f))<0.2)&&(TMath::Abs((BB.tr.y[]+0.97*BB.tr.ph[])-(BB.ts.ps.y+%f))<0.19))",psx_offset,psy_offset);

with psy_offset = 0.01 meters


-Matt