On theoretical uncertainties of the W boson mass measurement at LEP2

We discuss theoretical uncertainties of the measurement of the W boson mass at LEP2 energies, reconstructed with the help of the tandem of the Monte Carlo event generators KoralW and YFSWW3. Exploiting numerical results obtained with these programs, and the existing knowledge in the literature, we estimate that the theoretical uncertainty of the W mass due to electroweak corrections, as reconstructed at LEP2 with the help of these programs, is ∼5 MeV. Since we use certain idealized event selections and a simple MW-fitting procedure, our numerical exercises can be (should be) repeated for the actual “MW extraction methods” of the LEP2 measurements, using KoralW and YFSWW3 or other Monte Carlo programs.