[d2n-analysis-talk] T2,T6 time walk

[posik at jlab.org]

 Hi Brad,

   I was looking at the time walk of the T2 trigger (BB cerenkov + BB
Shower) and for run 2060 I find a similar behaviour as the one shown in
the last d2n meeting (time_walk.png) The y-axis is the DBB.t2[0]
variable (un-prescaled T2 trigger) and the x-axis is the
DBB.BBcerT06[0] variable (TDC 6 signal). So to correct this time walk I
figured I was going to need the characteristics of that linear line, so
I went ahead and made a linear fit (p1 fit, t2:TDC6.png) and found:

parameter      value
  0	      2.994628e+02   (const)
  1	      9.922598e-01   (slope)

  I also wanted to see what the un-prescaled t2 and t6 look like
(t2vst6.png) where T2 is the y-axis and T6 is the x-axis. I also tried
to plot the variable DBB.l1a , but I just get a white canvas and zero
entries. I was wondering is this because DBB.l1a is an un-prescaled
variable and the l1a triggeres only for prescaled triggers? Or is this a
crate map type error?  There is also a variable called DBB.f1l1a which I
assume is the l1a going to f1 TDC?

 I am a little confused on how to actually go about correcting for this
time walk effect. Do I apply corrections to the t2 vs TDC or do I really
want to correct the t2 vs t6 since t2 is our primary trigger?

 Also I am a bit concerned with ~95% of my statistics being lost with a
one track cut(BB.tr.n==1). Could this be a problem with the optics or
mwdc data files? Diana are you also seeing a large decrease in statistics
with this cut?

Thanks
Matt
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