Measurements of the top-quark mass using charged particle tracking

TL;DR

Three calorimeter-independent measurements of the top-quark mass in ttbar events are presented in the lepton+jets channel, using the mean transverse decay length (Lxy) of b-tagged jets and the mean transverse momentum of leptons from W decays, with track-based jet energies to minimize jet-energy-scale systematics. The analysis relies on corrections to the signal simulation (PDF reweighting, Lxy calibration, track-based jet energies) and data-driven background modeling, followed by single-variable and two-variable (Lxy and lepton p_T) pseudoexperiments to extract mt. The individual results are mt(Lxy)=166.9^{+9.5}_{-8.5} GeV/c^2 and mt(p_T)=173.5^{+8.8}_{-8.9} GeV/c^2, with a combined mt=170.7 ± 6.3 (stat) ± 2.6 (syst) GeV/c^2, representing a substantial reduction in jet-energy-scale systematics and providing a robust cross-check of calorimeter-based methods. The work suggests further gains are possible with improved luminosity profiles, lepton-momentum calibration, and continued refinement of track-based techniques, highlighting an important path for precision top-quark physics at hadron colliders.

Abstract

We present three measurements of the top-quark mass in the lepton plus jets channel with approximately 1.9 fb-1 of integrated luminosity collected with the CDF II detector using quantities with minimal dependence on the jet energy scale. One measurement exploits the transverse decay length of b-tagged jets to determine a top-quark mass of 166.9+9.5-8.5 (stat) +/- 2.9 (syst) GeV/c2, and another the transverse momentum of electrons and muons from W-boson decays to determine a top-quark mass of 173.5+8.8-8.9 (stat) +/- 3.8 (syst) GeV/c2. These quantities are combined in a third, simultaneous mass measurement to determine a top-quark mass of 170.7 +/- 6.3 (stat) +/- 2.6 (syst) GeV/c2.

Figures (13)

• Figure 1: Distributions of our measurement variables for simulated $t\bar{t}$ events after passing our event selection for top-quark masses separated by $50\ \textnormal{GeV}/c^2$. These distributions are normalized to unit area.
• Figure 2: Signal, background, and data for the Lxy and lepton $p_T$ distributions passing full event selection under hypothesized top-quark masses that are close to the measured results. The left plot is for the Lxy measurement, using top-quark mass $168\ \textnormal{GeV}/c^2$, and the right plot is for the lepton $p_T$ measurement, using top-quark mass $173\ \textnormal{GeV}/c^2$.
• Figure 3: Background prediction compared with data (black points) in the one-jet control region for Lxy (left) and lepton $p_T$ (right).
• Figure 4: Background prediction compared with data (black points) in the two-jet control region for Lxy (left) and lepton $p_T$ (right).
• Figure 5: (a): The distributions of track-based jet transverse energy divided by the photon $p_T$ for events with photon $p_T$ between $30\ \textnormal{GeV}/c$ and 40 $\textnormal{GeV}/c$. (b): The mean fraction of track-based jet transverse energy / photon $p_T$ for Pythia (red) and the data (blue) as a function of the measured photon transverse momentum (assumed to be the true jet transverse energy). The ratio of these trends between data and simulation is fitted to a line which is then used to correct measured track jet energies in the simulation.