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Interface to CBMROOT of littrack

main() function

CbmLitFindGlobalTracks is a main task to be called from macro in order to execute littrack tracking routines. The task automatically determines detector layout based on TGeo and configures track reconstruction in the TRD and MUCH detectors and hit-to-track merging in TOF.


// Tracking method to be used
// "branch" - branching tracking
// "nn" - nearest neighbor tracking
// "nn_parallel" - parallel implementation of nearest neighbor tracking
// Hit-to-track merger method to be used
// "nearest_hit" - assigns nearest hit to the track
void SetMergerType(const string &mergerType)
void SetTrackingType(const string &trackingType)

Field approximation

Polynomial field approximation is used in parallel tracking algorithm. Calculation of the polynomial coefficients for a specified field slice is implemented in the CbmLitFieldFitter class. Two options are implemented:

  • Usage of Minuit for minimization of squared error between polynom approximation and field map;
  • "Hand made" approximation based on least squares method.

The algorithm is able to approximate the field with polynomials of order 0 to 10. The default polynom order used in the tracking is 7.


Int_t polynomDegree = 7; // Polynom order
Double_t zPos = 100; // Z position of the slice [cm]
std::vector<Double_t> cx, cy, cz; // Polynom coefficients for Bx, By, Bz respectively
CbmLitFieldFitter* fitter = new CbmLitFieldFitter(polynomDegree);
fitter->FitSlice(zPos, cx, cy, cz);
Implementation of the polynomial field approximation.
void FitSlice(float Z, lit::parallel::LitFieldSlice< T > &slice)
Fits (X, Y) slice of the magnetic field at Z position.