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 (1992-1996) measurements with the most recent preliminary Run-II (2001-present) measurements using up to 750 pb{sup -1} of data. Taking correlated uncertainties properly into account the resulting preliminary world average mass of the top quark is M{sub t} = 172.5 {+-} 1.3(stat) {+-} 1.9(syst) GeV/c{sup 2}, which corresponds to a total uncertainty of 2.3 GeV/c{sup 2}. The top-quark mass is now known with a precision of 1.3%--a 20% improvement relative to the previous combination.