A pre-identification for electron reconstruction in the CMS particle-flow algorithm

In the CMS software, a dedicated electron track reconstruction algorithm, based on a Gaussian Sum Filter (GSF), is used. This algorithm is able to follow an electron along its complete path up to the electromagnetic calorimeter, even in the case of a large amount of Bremsstrahlung emission. Because of the significant CPU consumption of this algorithm, it can, however, only be run on a limited number of candidates. The standard GSF electron track reconstruction is triggered by the presence of high energy isolated electromagnetic clusters, but it is not suited for electrons in jets (usually soft and not isolated). A pre-identification algorithm based on both the tracker and the calorimeter, was therefore recently developed. It allows electron tracks within jets to be efficiently reconstructed even for small electron transverse momentum. This algorithm as well as its performance in terms of efficiency, mis-identification probability are presented.