Refitting Tracks

• The only known problems in the Production final fit are an underestimation of the material used in the fit and value of the magnetic field applied. A refit is necessary to get the best energy loss corrections. A correction for the magnetic field is usually called in ctmvft. A refit should only be necessary for analysis such as B mass measurements where, with the corrections, sub MeV precision can be achieved.


• Simulated data should also be refit using the same constants as in data. The simulation should be made using the standard cdfSim tcl.


• We recommend the TrackRefitter class for refitting tracks.


• A good example of how to use TrackRefitter is given in the TrackingUsageExample module in the TrackingUserMods package.


• Prerequisites
• Silicon Tracks, usually from the CdfTrackColl: PADTracks and the SiHitSet
• You must also puff the silicon hits(should be default unless you override the puffOnly statement)


• Tracking group recommendations on how to refit tracks
• We recommend to refit using:
• The F_KAL refitting mode(in kal proxy geometry mode - default)
• The default scaling called from the TrackRefitter class
• Using the Phantom layer with the parameters as blessed in the joint physics meeting(4.8.4) or the BPAK meeting (5.1 and 5.3 series)

talk GeometryManager
SiliconGeometryMenu
CreatePhantomLayer set t
exit
exit

For PhantomLayer parameters see see note 6355 for 4.8.4 and note 6905 for 5.1 and 5.3. Some more info and tcl are found here.


• Dropping only L00 hits
• Using the calibration pass table to load the alignment table or tables appropriate for your release:

# Example: Call Pass calibration table: ??
talk CalibrationManager
ProcessName set PROD_PHYSICS_CDF
PassName set ??
exit
# Print the alignment table so you have a record of what you used
module talk GeometryManager
SiliconGeometryMenu
AlignmentSource set "default"
AlignmentPrint set 2
exit
exit


• Optionally you can use the refitter in F_KAL mode with the SiliMap geometry: see note 5846
• The W mass group is working on using SiliMap
• Since SiliMap is a detailed map of the GEANT geometry it is both fast and more accurate than the Kal proxy geometry
• To use SiliMap there are some initializations necessary
• After setting up the cdf software setup the SiliMap product: setup silimap v5_3_1
• Initialize SiliMap before your first instance of the TrackRefitter is called: KalConverter::useSiliMap(true);
The proper headers should be included in the by including TrackRefitter header
• Turn on reading the SiliMap root file in your GeometryManager, SiliconGeometry sub menu talkto: ReadSiliMapROOT set t
• Note you can not switch between the SiliMap and the Kal Proxy geometry on the fly using the useSiliMap switch.


• Using the TrackExtrapolator to extrapolate track error to the beamline positions can improve the covariance matrix errors. The use of TrackExtrapolator has been studied in high pt physics. See cdf note 6824.


• Your physics group may have other recommendations


• Notes
  • Chi squared and Number of Degrees of freedom
  • chi2() - Combined COT Silicon chi squared
  • chi2CT() - COT portion of chi squared
  • chi2SI() - Silicon portion chi squared
    More exactly this is the chi squared of the fit starting with the covariance matrix of the COT and its 5 parameters as first measurement and adding the silicon measurement points.
  • numDegreesOfFreedom() - Number of degrees of freedom from the latest fit.
    Note that all silicon tracks are refit so this represents the number of silicon measurement points for OI and silicon standalone tracks
    Note that after running the silicon volume refit on COT track this number is 0.
    Look at the original COT track to find the number of degrees of freedom from the original COT fit.
  • chiSquared() - Temporary result constructed during pattern recognition and kept for debugging purposes. Note that this is not a standard member of CdfTrack but rather a member of the subclass SimpleReconstructedTrack - do not use this.
  • In 4.10.4 and earlier chi2SI was used to overwrite chi2. To get the original COT chi2 you had to go back to the original COT track.
  • Always make sure to keep up to date with the tracking known problems list: Current known tracking problems