[d2n-analysis-talk] Updated BB Momentum Code added to CVS and d2n.jlab.org

[Brad Sawatzky]

Diana's updated BB momentum reconstruction code has been added to
CVS and to d2n.jlab.org.

The libBigBite.so library in /usr/local had been rebuilt.  If you have a
symlink to that file in your personal directory you should be fine.  If
not, you will need to replace your personal copy with (a link to) the
updated version.

Diana's notes follow.

-- Brad

----- Forwarded message from Diana Parno <dparno at cmu.edu> -----

From: Diana Parno <dparno at cmu.edu>
Subject: New Momentum Code
To: Brad Sawatzky <brads at jlab.org>

Hi Brad,

Here are three files containing the new optics code for d2n. These all
belong in d2n_analysis/d2n/bigbitelib and replace Transversity-build
files with the same names. Could you place these in the CVS repository
and in /usr/local?

Here's a summary of the changes:

a. Rolled back to first-order momentum (positive and negative)
b. Added additional factor of 1.041 for negative optics.
c. Added smoothing function to low-momentum correction (positive and
negative)
d. Removed energy loss from momentum calculation.
e. New "BB.optics.p_firstorder" variable gives tree access to momentum
BEFORE low-momentum correction, for future flexibility.
f. Changed sign on final value of TargetTheta, in order to give it a
sign consistent with detector coordinate system.

This summary is also in the header of THaOpticsE06010.cxx.

I've replayed several production runs from different periods with this
code and don't see any problems. The positive-momentum spectrum looks
a bit strange for later runs, but Gregg and I think that's in the data
rather than in the code. There may be future modifications, depending
on Gregg's simulations of, say, where the delta should be, but now
that we're outputting a preliminary momentum variable as a matter of
course, these adjustments can be made post-replay if necessary. I
think this is a good point at which to roll out a better, d2n copy of
the momentum reconstruction, even if another copy has to be rolled out
later.

(I did check on the proton peak position using only T1 data, as we
discussed last week; no changes to the optics were necessary in order
to land the T1 proton peak well within an MeV of where we expected.)

There is also a "theoptics.cxx" file in bigbitelib, but it consists
solely of an #include statement and did not require modification.

Thanks,
Diana

-- 
Brad Sawatzky, PhD <brads at jlab.org>  -<>-  Jefferson Lab / Hall C / C111
Ph: 757-269-5947  -<>-  Fax: 757-269-5235  -<>- Pager: brads-page at jlab.org
The most exciting phrase to hear in science, the one that heralds new
  discoveries, is not "Eureka!" but "That's funny..."   -- Isaac Asimov