From 4df45162ec04df90f5c8412c552de14703f980dd Mon Sep 17 00:00:00 2001 From: belikov Date: Wed, 23 Jul 2008 14:20:01 +0000 Subject: [PATCH] Comments explaining the meaning of the different track parameters stored in the ESD tracks (Marian) --- STEER/AliESDtrack.cxx | 93 +++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 93 insertions(+) diff --git a/STEER/AliESDtrack.cxx b/STEER/AliESDtrack.cxx index ca815f5718e..7dedbe632d0 100644 --- a/STEER/AliESDtrack.cxx +++ b/STEER/AliESDtrack.cxx @@ -18,6 +18,99 @@ // This is the class to deal with during the phisics analysis of data // Origin: Iouri Belikov, CERN // e-mail: Jouri.Belikov@cern.ch +// +// +// +// What do you need to know before starting analysis +// (by Marian Ivanov: marian.ivanov@cern.ch) +// +// +// AliESDtrack: +// 1. What is the AliESDtrack +// 2. What informations do we store +// 3. How to use the information for analysis +// +// +// 1.AliESDtrack is the container of the information about the track/particle +// reconstructed during Barrel Tracking. +// The track information is propagated from one tracking detector to +// other using the functionality of AliESDtrack - 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. +// +// Kalman filter take into account additional effect which are +// difficult to handle using global fit. +// Effects: +// a.) Multiple scattering +// b.) Energy loss +// c.) Non homogenous magnetic field +// +// In general case, following barrel detectors are contributing to +// the Kalman track information: +// a. TPC +// 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. +// +// +// 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) +// 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 +// 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 *GetInnerParam() const { return fIp;} +// +// 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 +// 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: +// 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;} +// //----------------------------------------------------------------- #include -- 2.43.0