Analytic formula for track extrapolation in non-homogeneous magnetic field

The paper describes track propagation through non-homogeneous magnetic field using an analytic expression. The analytic formula has been derived under very general assumptions on a magnetic field. Precision of extrapolation does not depend on the shape of the magnetic field. Results of the implementation in the CBM track fitting procedure based on the Kalman filter are presented and compared with the extrapolation based on the fourth-order Runge–Kutta method.