[d2n-analysis-talk] Trigger Offset for S1, S2m Paddles?

[David Flay]

Hey Brad,

I was poking around the source code, and I've found an interesting
quantity in the THaScintillator class: a data member called fTrigOff,
which eventually finds its way into the ROOTfile as L.s2.troff (for S2m,
for instance).  It's labeled as a 'trigger offset for paddles.'  Looking
at the source code, it shows up in the ReadDatabase method (after it's
been initialized to 0):

  while ( ReadComment( fi, buf, LEN ) ) {}
  // trigger timing offsets
  {
    int cnt=0;
    while ( cnt<fNelem && fgets( buf, LEN, fi ) && ! strchr(buf,'[') ) {
      char *ptr = buf;
      int pos=0;
      while ( cnt < fNelem && sscanf(ptr,"%lf%n",&fTrigOff[cnt],&pos)>0 ) {
	ptr += pos;
	cnt++;
      }
    }
  }

this part of the code follows the part where the timewalk correction
parameters are read into its corresponding data member.  Could this be a
quantity that has been left out of the db_L.s2.dat file (as there is no
quantity referring to a trigger offset for each paddle listed)?  Have you
seen this variable before?

I was thinking maybe this variable is read into the THaScintillator class,
but used elsewhere, since that's all that is done with that variable
here...

Maybe this variable has something to do with what Vince says (at the very
end of this wiki post:
https://hallaweb.jlab.org/wiki/index.php/Left_HRS_Scintillator_Timing)
where he says:

"The S1 time substructure is apparently due to time jitter between the S2m
paddles that eventually form the T3 trigger time. The left HRS T3 time is
closely tied to the timing for the right-side of S2m, since this side is
self-timing. Ideally all the S2m trigger cables on the right side are the
same length and all electronic channels have the same delay, but clearly
they are not and lead to the sub-structure seen in the S1 timing. This can
be corrected in software with a special correction. However this should
not matter for the coincidence time, and only affects the left HRS beta
spectrum."

Of course, we know about the opening few sentences.  The comment about a
'special correction' is what I'm curious about.

I'm just looking for other possible things to assist in the process,
considering that the s2m times are indeed aligned correctly (I sent these
plots out last weekend), and I've also aligned the S1 times, to make
things simpler to consider when examining the S2m time - S1 time.

Dave

-------------------------------------------------
David Flay
Physics Department
Temple University
Philadelphia, PA 19122

office: Barton Hall, BA319
phone: (215) 204-1331

e-mail: flay at jlab.org
            flay at temple.edu

website: http://www.jlab.org/~flay
              http://quarks.temple.edu
-------------------------------------------------