[Halld-offline] Recreating tracks

Simon Taylor staylor at jlab.org
Thu Aug 7 15:00:02 EDT 2014

Hi, Matt.

Regarding moving the resolution of the "missing track hypothesis" 
problem to the tracking code itself, yes, this is doable.  Of course I 
would prefer that the fit itself work for each track hypothesis, but in 
the absence of this I will implement a fix to fill in the gaps using 
existing track information.


On 08/07/2014 02:51 PM, Matthew Shepherd wrote:
> Hi Paul,
> I'm cc'ing this one to the Hall D offline list since
> I suspect it has implications on other software systems
> like tracking.
> As you know Ryan and I have been working to both
> learn your analysis framework and cross check with
> some other high level analysis code that Ryan has
> that we used for BES and CLEO to reconstruct
> many reactions.
> We are still at the stage of trying to get consistent
> results for what we think are the same cuts running
> over the same events.
> So far the biggest issue we see (I think) is related to
> the recreation of track hypotheses for tracks that did
> not contain a hypothesis at the time the initial tracking
> is done.  For example, track candidate has a proton
> fit but not a pion fit so you have a special factory that
> reconstructs the pion fit from the proton fit (not the hits)
> so it can be used in analysis.
> It seems this makes a notable difference for some
> topologies.  For example, gamma p -> 3 (pi+ pi-) p it
> seems that my signal efficiency, using your code, is
> something around 10x more than what is obtained
> with the "stock" tracks provided by the reconstruction
> framework.
> There are several problems/issues with this:
> * Tracks are something that should be provided to
> all users.  As is, it is very hard for a user to get these
> recreated tracks, which seem to be, based on the
> efficiency gain, "real" tracks.  We've tried to cook
> up a factory that creates 5 DReactions each of which
> has a single track that triggers your factory create the
> track hypotheses, that Ryan can then extract, but
> this is non-trival and we still don't understand the
> results (see question below).
> * This is slooow to do at analysis time.  Your
> algorithm involves reswimming, which is really slow.
> We discussed some speed issues last week.
> I thought a lot of the slowness was in overhead
> in analysis classes, but I'm not sure.  When Ryan
> started to use the kludge to get the recreated tracks
> his code slowed down by 5x - 10x.  We shouldn't
> have to redo tracking at analysis... any redoing
> we are doing isn't nearly as good as what we
> could have done with the original hits.
> A question:  how is the FOM for newly created
> track hypotheses determined?  We see the pattern
> that some recreated tracks have an FOM of zero.
> These tracks are getting cut by Ryan's tracking
> FOM cut.  However, they don't seem to be cut
> by my specified FOM cut.  Does the analysis system
> ignore the FOM cut for tracks that it recreates
> from another hypothesis?
> It seems to me like we're trying to solve a tracking
> issue at the analysis stage and it is consuming a
> lot of analysis-time CPU resources and creating
> confusing for users.
> It seems we have a solution -- can we move it from
> the analysis libraries into the core tracking software?
> Matt
> ---------------------------------------------------------------------
> Matthew Shepherd, Associate Professor
> Department of Physics, Indiana University, Swain West 265
> 727 East Third Street, Bloomington, IN 47405
> Office Phone:  +1 812 856 5808
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