A new fast track-fit algorithm based on broken lines

The determination of the charged particle momentum in HEP experiments requires a fit of a parametrization to the points measured in a tracking chamber. A new non-recursive track-fit algorithm based on broken lines allows to reconstruct the particle trajectory taking into account details of multiple scattering. It provides optimal parameters and their covariance matrices at track start and end, and optimal values at each measured point along the trajectory including the variances. The parametrization of the trajectory allows the use of sparse-matrix techniques with a total computing time proportional to the number of data points. Under test conditions the new algorithm is found to be six times faster than the Kalman filter.