Measurement of the top quark mass in the lepton+jets channel using the Ideogram Method

A measurement of the top quark mass using events with one charged lepton, missing transverse energy, and jets in the final state, collected by the D0 detector from p-pbar collisions at sqrt{s} = 1.96 TeV at the Fermilab Tevatron collider, is presented. A constrained fit is used to fully reconstruct the kinematics of the events. For every event a top quark mass likelihood is calculated taking into account all possible jet assignments and the probability that an event is signal or background. Lifetime-based identification of b jets is employed to enhance the separation between t-tbar signal and background from other physics processes and to improve the assignment of the observed jets to the quarks in the t-tbar hypothesis. We extract a multiplicative jet energy scale factor JES in-situ, greatly reducing the systematic effect related to the jet energy measurement. In a data sample with an integrated luminosity of 425 pb-1, we observe 230 candidate events, with an estimated background of 123 events, and measure m_t = 173.7 +-4.4 (stat + JES) +2.1/-2.0 (syst) GeV. This result represents the first application of the Ideogram technique to the measurement of the top quark mass in lepton+jets events.