engleski

Electron Reconstruction in CMS

The CMS electron reconstruction algorithms and expected performance from a detailed Monte Carlo simulation are presented. The energy deposited in the electromagnetic calorimeter is measured in clusters of clusters (superclusters) which collect bremsstrahlung photons emitted in the tracker volume. Electron tracks are seeded using the innermost tracker layers. The ECAL driven seeding algorithm, optimised for isolated electrons in the $p_{;T};$ range relevant for Z or W decays and down to $p_{;T}; \simeq 5~$GeV/c, is complemented by a tracker driven seeding more suitable for low $p_{;T};$ electrons and/or electrons inside jets. Trajectories are reconstructed using a dedicated modeling of the electron energy loss and fitted with a Gaussian Sum Filter. Electron candidates are preselected using loose cuts on track-cluster matching observables so to preserve the highest possible efficiency while removing part of the QCD background. A cleaning is performed to resolve cases where several tracks are reconstructed from the conversion legs of radiated photons. The electron charge is determined by comparing different charge measurement observables to better cope with the mis-identification that arises from early conversions of radiated photons. Electrons are classified using observables sensitive to the pattern of bremsstrahlung emission and showering in the tracker material. The electron energy is deduced from a weighted combination of the supercluster energy and tracker momentum measurements based on the electron classes. The electron direction is that of the reconstructed electron track at the interaction point. The specific algorithms developed for the cases of low $p_{;T};$ electrons and non-isolated electrons are presented. Finally, possible effects of startup conditions of the LHC are discussed.

CMS; LHC; electrons

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