  The bremsstrahlung energy loss distribution of electrons propagating in
matter is highly non Gaussian. Because the Kalman filter relies solely on
Gaussian probability density functions, it might not be an optimal
reconstruction algorithm for electron tracks. A Gaussian-sum filter (GSF)
algorithm for electron track reconstruction in the CMS tracker has therefore
been developed. The basic idea is to model the bremsstrahlung energy loss
distribution by a Gaussian mixture rather than a single Gaussian. It is shown
that the GSF is able to improve the momentum resolution of electrons compared
to the standard Kalman filter. The momentum resolution and the quality of the
estimated error are studied with various types of mixture models of the energy
loss distribution.
