New Measurement of the Top Quark Mass in Lepton+Jets ttbar Events at DO

We present a new measurement of the mass of the top quark using lepton + jets ttbar events collected by the DO experiment in Run I of the Fermilab Tevatron Collider. The mass is extracted through a comparison of each event with a leading-order matrix element that depends on the top quark mass. 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.