A Combination of CDF and D0 Results on the Mass of the Top Quark

We summarize the top-quark mass measurements from the CDF and D0 experiments at Fermilab. We combine published Run-I measurements with the most recent Run-II measurements. Taking correlated uncertainties into account the resulting preliminary world average top-quark mass is Mt=170.9+/-1.1(sta)+/-1.5(sys) GeV/c2 assuming Gaussian systematic uncertainties. Adding in quadrature yields a total uncertainty of 1.8 GeV/c2, corresponding to a relative precision of 1.1% on the mass of the top quark.