Precision measurement of the top-quark mass from dilepton events at CDF II

We report a measurement of the top-quark mass, $M_t$, in the dilepton decay channel of $t\overline{t}\to b{\ell }^{\prime +}{\nu }_{{\ell }^{\prime }}\overline{b}{\ell }^{-}{\overline{\nu }}_{\ell }$ using an integrated luminosity of $1.0{\mathrm{fb}}^{-1}$ of $p\overline{p}$ collisions collected with the CDF II detector. We apply a method that convolutes a leading-order matrix element with detector resolution functions to form event-by-event likelihoods; we have enhanced the leading-order description to describe the effects of initial-state radiation. The joint likelihood is the product of the likelihoods from 78 candidate events in this sample, which yields a measurement of $M_t=164.5\pm 3.9(\mathrm{stat}.)\pm 3.9(\mathrm{syst}.)\mathrm{GeV}/c^2$, the most precise measurement of $M_t$ in the dilepton channel.

Figure 1

Left: Mean measured $M_t$ in Monte Carlo experiments of signal and background events at varying top-quark mass. The solid line is a linear fit to the points. Right: Pull widths of Monte Carlo experiments of signal and background events at varying top-quark mass. The solid line is the average of all points, $1.17\pm 0.02$.

Figure 2

Joint posterior probability density as a function of the top-quark mass for the 78 observed candidate events, after all corrections. Systematic uncertainties are not shown.