Extracting the Top-Quark Width from Nonresonant Production

In the context of the standard model of particle physics, the relationship between the top-quark mass and width (${\mathrm{\Gamma }}_t$) has been precisely calculated. However, the uncertainty from current direct measurements of the width is nearly 50%. A new approach for directly measuring the top-quark width using events away from the resonance peak is presented. By using an orthogonal dataset to traditional top-quark width extractions, this new method may enable significant improvements in the experimental sensitivity in a method combination. Recasting a recent ATLAS differential cross section measurement, we find ${\mathrm{\Gamma }}_t=1.28\pm 0.30\mathrm{GeV}$ ($1.33\pm 0.29\mathrm{GeV}$ expected), providing the most precise direct measurement of the width.

Figure 1

The $m_{b\ell }^{\text{minimax}}$ spectrum predicted using b_bbar_41 is shown for various values of the top-quark width. Data from the unfolded ATLAS measurement are included for comparison. The gray band shows the theoretical uncertainty for the simulated sample corresponding to the predicted SM value of the width.

Figure 2

Observed and expected top-quark widths for the b_bbar_41 and MG5_aMC@NLO signal models.