//
// 1.AliESDtrack is the container of the information about the track/particle
// reconstructed during Barrel Tracking.
+// Content:
+// a.) Track parameters and covariance - AliExternalTrackParam - snapshots along trajectory at differnt tracking steps
+// current, fIp, fTPCinner, fCp, fOp, fHMPIDp, + friendTrack (fITSout, fTPCout, fTRDin)
+// b.) Flags - per detector status bits
+// c.) Track fit quality -chi2, number of clusters
+// d.) Detector PID information
+// d.) Different detector specific information (e.g number of tracklets in TRD, TOF cluster descriptor ...)
+//
+//
// The track information is propagated from one tracking detector to
-// other using the functionality of AliESDtrack - Current parameters.
+// other using the functionality of AliESDtrack (AliExternalTrackParam - current parameters)
//
-// No global fit model is used.
-// Barrel tracking use Kalman filtering technique, it gives optimal local
-// track parameters at given point under certian assumptions.
+// Barrel tracking uses Kalman filtering technique (no global fit model is used). Kalman provides optimal local
+// track parameters estimate at given position under certian assumptions.
+// Following approximations were used:
+// a.) gaussian Multiple scattering
+// b.) gaussian energy loss
+// c.) gaussian error of the space point residuals
//
-// Kalman filter take into account additional effect which are
-// difficult to handle using global fit.
-// Effects:
+// Kalman filter take into account following effects which are
+// difficult to handle using global fit:
// a.) Multiple scattering
// b.) Energy loss
// c.) Non homogenous magnetic field
// b. ITS
// c. TRD
//
-// In general 3 reconstruction itteration are performed:
-// 1. Find tracks - sequence TPC->ITS
-// 2. PropagateBack - sequence ITS->TPC->TRD -> Outer PID detectors
-// 3. Refit invward - sequence TRD->TPC->ITS
-// The current tracks are updated after each detector (see bellow).
-// In specical cases a track sanpshots are stored.
-//
+// Track findind/fitting procedure is done in 3 steps:
+// 1. Cluster2Track(in) - inward sequence TPC->ITS
+// 2. PropagateBack(out) - outward sequence ITS->TPC->TRD -> Outer PID detectors
+// 3. RefitInward(refit) - inward sequence TRD->TPC->ITS
+// After each recosntruction step detector status is updated in the data member fFlags
+// fFlags|=k<DetectorName><step> where step={1:in,2:out,3:refit,}
+// For some of detectors a special flags were implemented. Declaration of list of all flags can be find in $ALICE_ROOT/STEER/STEERBase/AliVTrack.h
+//
+//
+// The current track parameter is updated after each detector (see bellow).
+// In specical cases a track snapshots (AliExternalTrackParam) are stored
//
+//
// For some type of analysis (+visualization) track local parameters at
// different position are neccesary. A snapshots during the track
-// propagation are created.
-// (See AliExternalTrackParam class for desctiption of variables and
-// functionality)
+// propagation are created and stored either in track itself (for analysis purposes) or assiciated friend track (for calibration and debugging purposes)
+// (See AliExternalTrackParam class for desctiption of variables and functionality)
// Snapshots:
-// a. Current parameters - class itself (AliExternalTrackParam)
-// Contributors: general case TRD->TPC->ITS
-// Preferable usage: Decission - primary or secondary track
-// NOTICE - By default the track parameters are stored at the DCA point
-// to the primary vertex. optimal for primary tracks,
-// far from optimal for secondary tracks.
-// b. Constrained parameters - Kalman information updated with
-// the Primary vertex information
-// Contributors: general case TRD->TPC->ITS
-// Preferable usage: Use only for tracks selected as primary
-// NOTICE - not real constrain - taken as additional measurement
-// with corresponding error
+// a.) Current parameters (AliESDtrack itself)
+// Description: as obtained in the last succesfull tracking step
+// Contributors: best case TRD->TPC->ITS after RefitInward
+// Recomended way to get track parameters. It includes all of the information.
+// NOTICE - By default the track parameters are stored at the DCA point to the primary vertex.
+// Optimal for primary tracks, far from optimal for deeply secondary tracks.
+// To get optimal track parameters at the secondary vertex, OnTheFly V0s with associated track parameters should be used
+//
+// b.) Constrained parameters (fCp)
+// Description:
+// Kalman track updated with the Primary vertex information with corresponding error (soft constraint - see http://en.wikipedia.org/wiki/Constraint_(mathematics)#Hard_and_soft_constraints)
// Function:
-// const AliExternalTrackParam *GetConstrainedParam() const {return fCp;}
-// c. Inner parameters - Track parameters at inner wall of the TPC
-// Contributors: general case TRD->TPC
-// function:
+// const AliExternalTrackParam *GetConstrainedParam() const {return fCp;}
+// Contributors: best case TRD->TPC->ITS after RefitInward
+// Recommended usage: Use only for tracks selected as primary (check GetConstrainedChi2())
+// NOTICE - not real constraint only soft constraint
+//
+// c.) Inner parameters (fIp) -
+// Description: Track parameters at inner wall of the TPC
+// Function:
// const AliExternalTrackParam *GetInnerParam() const { return fIp;}
+// Contributors: general case TRD->TPC (during RefitInward)
+// Recomended usage: To provide momenta for the TPC PID and to estimate quality of the track determination for further
+//
+// d.) TPCinnerParam (fTPCinner):
+// Description: TPC only parameters at DCA to the primary vertex (corrected for the material between TPC and vertex)
+// Function:
+// const AliExternalTrackParam *GetTPCInnerParam() const {return fTPCInner;}
+// Contributors: TPC only from in step 1 (Cluster2Tracks)
+// Recomended usage: Requested for HBT study
+// (smaller correlations as using also ITS information)
+// NOTICE: Optimal for primary, far from optimal for secondary tracks (similar to track parameters a.)
+// ! We should always use the c.) fIp in case of the TPC PID analysis, or undo material budget correction!
//
-// d. TPCinnerparam - contributors - TPC only
-// Contributors: TPC
-// Preferable usage: Requested for HBT study
-// (smaller correlations as using also ITS information)
-// NOTICE - the track parameters are propagated to the DCA to
-// to primary vertex
-// Optimal for primary, far from optimal for secondary tracks
+// e.) Outer parameters - (fOp)
+// Description: track parameters during PropagateBack in the last sucessfull propagation
+// Reason to generate backup OuterParameters
+// a.) Local inclination angle bigger than threshold -
+// Low momenta tracks
+// b.) Catastrofic (large relative>~20 %)energy loss in material outside of the TPC
+// c.) No additional space points contributing to track
// Function:
-// const AliExternalTrackParam *GetTPCInnerParam() const {return fTPCInner;}
-//
-// e. Outer parameters -
-// Contributors- general case - ITS-> TPC -> TRD
-// The last point - Outer parameters radius is determined
-// e.a) Local inclination angle bigger than threshold -
-// Low momenta tracks
-// e.a) Catastrofic energy losss in material
-// e.b) Not further improvement (no space points)
-// Usage:
+// const AliExternalTrackParam *GetOuterParam() const { return fOp;}
+// Contributors: general case - ITS-> TPC -> TRD ( during PropagateBack )
+// Recomended usage:
// a.) Tracking: Starting parameter for Refit inward
// b.) Visualization
// c.) QA
// NOTICE: Should be not used for the physic analysis
-// Function:
-// const AliExternalTrackParam *GetOuterParam() const { return fOp;}
//
//-----------------------------------------------------------------
git://git.uio.no / u / mrichter / AliRoot.git / commitdiff