New measurement of the top quark mass in lepton + jets $t\bar{t}$ events at D\O

We present a new measurement of the mass of the top quarkusing lepton + jets ttbar events collected by the DO experiment in Run I of the Fermilab TevatronCollider. The mass is extracted through a comparison of each event with a leading-order matrix element that depends on the top quarkmass. The result is M_t=180.1 +/- 3.6 ( stat) +/- 3.9 (sys) GeV/c^2. Combining this improved measurement with our previous value from dilepton channels yields the new DO result M_t=179.0 +/- 3.5 ( stat) +/- 3.8 (sys) GeV/c^2.