Direct measurement of the top quark mass by the DØ collaboration

Abstract

We determine the top quark mass m_t using tt̅ pairs produced in the DØ detector by √s=1.8TeV pp̅ collisions in a 125pb^-1 exposure at the Fermilab Tevatron. We make a two constraint fit to m_t in tt̅ →bW+b̅ W- final states with one W boson decaying to qq̅ and the other to eν or µν. Likelihood fits to the data yield m_t(l+jets)=173.3±5.6 (stat) ± 5.5 (syst) GeV/c². 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/c². 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/c², consistent with the above result. Studies of kinematic distributions of the top quark candidates are also presented. 14.65.Ha, 13.85.Ni, 13.85.Qk.