Reconstruction of decayed particles based on the Kalman filter

The note describes a reconstruction package for fitting decayed particles. The package is based on the Kalman filter. The Kalman filter procedure has been modified in order to operate with an extended model of measurements and to filter by an optimum measurement. The reconstructed decayed particle contains all necessary information about the particle both at the point of its generation and at the point of its decay. Therefore, the developed method is suitable both for the complete reconstruction of decayed particles and for the reconstruction of vertices only. Results of tests of the reconstruction package are presented and discussed.