We determine the top quark mass m(t) using t (t) over bar pairs produced in the D empty set detector by root s = 1.8 TeV p (p) over bar collisions in a 125 pb(-1) exposure at the Fermilab Tevatron. We make a two constraint fit to m(t) in t (t) over bar-->bW(+)(b) over bar W- final states with one W boson decaying to q (q) over bar and the other to e nu or mu nu. Likelihood fits to the data yield m(t)(l + jets) = 173.3 +/- 5.6 (stat) +/- 5.5 (syst) GeV/c(2). When this result is combined with an analysis of events in which both W bosons decay into leptons, we obtain m(t) = 172.1 +/- 5.2 (stat) +/- 4.9 (syst) GeV/c(2) An alternate analysis, using three constraint fits to fixed top quark masses, gives m(t)(l + jets) = 176.0 +/- 7.9 (stat) +/- 4.8 (syst) GeV/c(2), consistent with the above result. Studies of kinematic distributions of the top quark candidates are also presented. [S0556-2821(98)06815-5].
