sPHENIX tracking discussion

["Pereira Da Costa, Hugo Denis Antonio" <hugo.pereira-da-costa AT lanl.gov>]

All, (especially Joe, Tony)

I am looking into analyzing our ‘golden’ zero-field runs.

I am confused about which code is responsible for doing the straight line fit of our clusters in that configuration.

Right now the only instance that I have found is in TrackResiduals::lineFitClusters(). Is that all there is ?

This fit ignores errors on the cluster position, thus handling MVTX, INTT and TPC clusters on the same footage. This is subobtimal for qualifying misalignments.

It also ignores TPOT clusters, probably for the same reason. (because TPOT detectors are 1D, one of the coordinate has an error as large as the strip length and the cluster position at the middle of the strip. Ignoring the error will break the fit.)

Is there any other, more correct, alternative around ?

If not: I have some old code that I can easily repurpose that would do a proper fit to the clusters accounting for their uncertainties. (this boils down to a simple 4x4 matrix inversion really)

Note that ideally, an ACTS (or GENFIT) straight line fit would be even better than this, because it would properly handle the  material budget in addition to the cluster uncertainties.

 

Finally: is TrackResiduals really the right place to do such a fit, and should we not rather write a dedicated module, similar to PHActsTrackFitter ? This would allow all evaluators to run on straight track fits (including my own), and not just PHTpcResiduals.

 

Comments ?

 

Hugo