Parton Distribution Uncertainty In The Measurement Of Mw In Proton Antiproton Collisions

We show explicitly how the value of the W boson mass, M w , measured at the p p ̄ colliders depends on the choice of parton distributions used in the fitting procedure, and demonstrate why the error from this source (of order ±50 MeV or less) is considerably smaller than was previously believed. Recent deep inelastic muon scattering data on the structure function ratio F 2 μ n / F 2 μ p play a key role in reducing this uncertainty on M w .