The systematic errors for single W production in ALEPH at generator level based on KoralW/Grace comparisons

In the ALEPH experiment at LEP2, KoralW is used to generate single W events. The goal of this note to compare the KoralW generator to Grace which was already validated for single W. The study is done at generator level for an energy of 200.0 GeV. An agreement of 5% on the total single W cross-section is obtained. The photon contamination in the detector acceptance, which decreases the selection efficiency, is computed for both generators. In addition (for ALEPH single W cross section paper), the correction factor between the single W cross sections with the LEP or ALEPH single W definitions are shown.