First Simultaneous Measurement of the Top Quark Mass in the Lepton + Jets and Dilepton Channels at CDF

We present a measurement of the mass of the top quark using data corresponding to an integrated luminosity of 1.9 fb-1 of p anti-p collisions collected at s**(1/2) =1.96 TeV with the CDF II detector at Fermilab's Tevatron. This is the first measurement of the top quark mass using top-antitop pair candidate events in the lepton + jets and dilepton decay channels simultaneously. We reconstruct two observables in each channel and use a non-parametric kernel density estimation technique to derive two-dimensional probability density functions from simulated signal and background samples. The observables are the top quark mass and the invariant mass of two jets from the W decay in the lepton + jets channel, and the top quark mass and the scalar sum of transverse energy of the event in the dilepton channel. We perform a simultaneous fit for the top quark mass and the jet energy scale, which is constrained in situ by the hadronic W boson mass. Using 332 lepton + jets candidate events and 144 dilepton candidate events, we measure the top quark mass to be M_top =171.9 +/- 1.7(stat. + JES) +/- 1.1 (other syst.) GeV/c2