Measurement of the top quark mass in $p\overline{p}$ collisions at $\sqrt{s}=1.96\mathrm{TeV}$ using the decay length technique

We report the first measurement of the top quark mass using the decay length technique in $p\overline{p}$ collisions at a center-of-mass energy of 1.96 TeV. This technique uses the measured flight distance of the $b$ hadron to infer the mass of the top quark in lepton plus jets events with missing transverse energy. It relies solely on tracking and avoids the jet energy scale uncertainty that is common to all other methods used so far. We apply our novel method to a $695{\mathrm{pb}}^{-1}$ data sample recorded by the CDF II detector at Fermilab and extract a measurement of $m_t={180.7}_{-13.4}^{+15.5}(\mathrm{stat}.)\pm 8.6(\mathrm{syst}.)\mathrm{GeV}/c^2$. While the uncertainty of this result is larger than that of other measurements, the dominant uncertainties in the decay length technique are uncorrelated with those in other methods. This result can help reduce the overall uncertainty when combined with other existing measurements of the top quark mass.

Figure 1

Comparison of $L_{2D}$ of positive tags from observed data and dijet MC in events with two secvtx tags and an identified electron or muon in one of the two tagged jets. Both the lepton tag and the nonlepton tag are included. Both distributions are normalized to unit area.

Figure 2

Most-probable (solid) and $\pm 1\sigma$ (broken) $m_t$ curves as a function of $⟨L_{2D}⟩$. Uncertainties are statistical only. Measured $⟨L_{2D}⟩$ is overlaid as dashed line.

Figure 3

The $L_{2D}$ distribution of positive tags in selected events. The points are the observed data. Expected contributions from signal and background MC are displayed cumulatively in the histogram. The MC is normalized to the observed data.