track attributes in Bdst

From: hagel@comp.tamu.edu
Date: Tue Jun 17 2003 - 12:03:05 EDT

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    Hello,
Interested parties probably read my message regarding the global track fitting
that I have implemented.  More details on that will emerge.  I have run into a
problem, however.  I made Bdst files thinking I was using that information and
then things did not make sense when I began to use them, so I started digging in
the code (again).  Here is what I find for the Bdst tracks unless I
misunderstand something.

1. theta, phi and vertices for BdstTrack are actually the theta, phi and vertex
of the BrFfsTrack extracted from the BrFsTrack and the information from the
BrFsTrack (as well as the information from the BrBfsTrack) is ignored/thrown
away.  That seems strange to me as I had read the code generating the BrFsTracks
to be an attempt to have the "global picture" which is made up of the compendium
of information from the BrFfsTracks and the BrBfsTracks.  That is where I set
the theta and phi that come out of that procedure.

2. There is no momentum information in the BdstTrack.  The only momentum saved
is in the momentum information from the BdstFsTrack::fD2, fD3 and fD4.  And
there is no possibility to save information from a global track ie the momentum
that you think is the best for the track.  I had niavely set the momentum of the
BrFsTrack to be the momentum that comes out of the fitting procedure only to see
it thrown away by the BdstModule::FillTrack.

I would like some comments on this.  I do realize that almost all (if not all)
of the information necessary to fit the tracks is saved in the BdstFsTrack.  But
if one waits until after the Bdst step to generate the fit tracks, the
possibility of using a perhaps better momentum to calculate pid or anything else
that one would use momentum for is precluded.  So at least for my personal copy,
I am going to add a BdstTrack:: momentum and I will fill the theta and phi with
the values I get out of the fit.  After I have comments I will weigh what to do
"officially"

Regards

Kris

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