[Halld-offline] Recreating tracks

Paul Mattione pmatt at jlab.org
Thu Aug 7 16:40:19 EDT 2014

One last thing: if the tracking NDF is zero, the tracking FOM cut is not placed.  

 - Paul

On Aug 7, 2014, at 4:35 PM, Paul Mattione wrote:

> For the tracking FOM: It just copies the chisq & ndf from whatever hypothesis it copied everything else from (p3, v3, etc.).  The hypothesis it copies from is determined by the DTrackTimeBased_factory_Combo::dParticleIDsToTry list.  If none of the PIDs to try is available, it just takes the track with the best overall FOM (dedx + timing) and uses that one.  
> - Paul
> On Aug 7, 2014, at 2:51 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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