Precision Top Quark Mass Measurement in the Lepton + Jets Topology in ppbar Collisions at sqrt(s) = 1.96 TeV

Abstract

We report two measurements of the top quark mass M_top using the CDF II detector at the Fermilab Tevatron in a 318 pb^-1 data sample observed in the lepton + jets final state. One method uses an event-based likelihood technique resulting in M_top = 173.2 +2.6/-2.4 (stat.) +/- 3.2 (syst.) GeV/c^2 or 173.2 +4.1/-4.0 GeV/c^2. The second method reconstructs a top quark mass in each event using the measured invariant mass of the hadronically decaying W boson to constrain the jet energy scale to obtain a value for M_top of 173.5 +3.7/-3.6 (stat.) +/- 1.3 (syst.) GeV/c^2 or 173.5 +3.9/-3.8 GeV/c^2. We take the latter, which is more precise, as our result.

Figures (3)

• Figure 1: The value of the top quark mass at the maximum of the DLM likelihood is plotted for each event. Data events (points) are compared to an expected distribution (histogram) comprising simulated $t\bar{t}$ ($\mathrm{M}_{\text{top}}$=$172.5~\mathrm{GeV}/c^{2}$) and background events. The last bin includes events with masses $>305~\mathrm{GeV}/c^{2}$. The inset shows the joint log-likelihood for the 63 events, before accounting for the presence of background.
• Figure 2: The $\mathrm{m}_{\mathrm{t}}^{\text{reco}}$ distribution of the template method is shown for each subsample overlaid with the expected distribution using $\mathrm{M}_{\text{top}}$, $\mathrm{JES}$ and signal and background normalizations from the combined fit. The events with $\chi^2>9$ have been excluded from each subsample.
• Figure 3: Contours of the template method likelihood are shown in the $\mathrm{M}_{\text{top}}$-$\mathrm{JES}$ plane for the combined fit to all four subsamples. The crosshair shows the best fit point. Contours are given at intervals of $\Delta\ln L$, the change in log-likelihood from its maximum.