Top-Quark Mass Measurement from Dilepton Events at CDF II

We report a measurement of the top-quark mass using events collected by the CDF II detector from $p\overline{p}$ collisions at $\sqrt{s}=1.96\mathrm{TeV}$ at the Fermilab Tevatron. We calculate a likelihood function for the top-quark mass in events that are consistent with $t\overline{t}\to \overline{b}{\ell }^{-}{\overline{\nu }}_{\ell }b{\ell }^{\prime +}{\nu }_{\ell }^{\prime }$ decays. The likelihood is formed as the convolution of the leading-order matrix element and detector resolution functions. The joint likelihood is the product of likelihoods for each of 33 events collected in $340{\mathrm{pb}}^{-1}$ of integrated luminosity, yielding a top-quark mass $M_t=165.2\pm 6.1(\mathrm{stat})\pm 3.4(\mathrm{syst})\mathrm{GeV}/c^2$. This first application of a matrix-element technique to $t\overline{t}\to b{\ell }^{+}{\nu }_{\ell }\overline{b}{\ell }^{\prime -}{\overline{\nu }}_{{\ell }^{\prime }}$ decays gives the most precise single measurement of $M_t$ in dilepton events. Combined with other CDF run II measurements using dilepton events, we measure $M_t=167.9\pm 5.2(\mathrm{stat})\pm 3.7(\mathrm{syst})\mathrm{GeV}/c^2$.

Figure 1

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.

Figure 2

Joint posterior probability density as a function of the top-quark mass for the 33 candidate events in data, after all corrections. Systematic uncertainties are not shown.