Direct Top-Quark Width Measurement CDF

TL;DR

This paper reports the first direct measurement of the top-quark width using $tar{t}$ events at Fermilab, setting upper and lower limits consistent with the Standard Model, based on a detailed analysis of lepton+jets decay channels.

Contribution

It introduces a novel method for directly measuring the top-quark width using template fits and in situ jet energy scale calibration in $par{p}$ collisions.

Findings

Upper limit on top-quark width: 7.6 GeV at 95% CL

Two-sided 68% CL interval: 0.3 GeV to 4.4 GeV

First direct measurement setting a lower limit on $\

Abstract

We present a measurement of the top-quark width using $t\bar{t}$ events produced in $p\bar{p}$ collisions at Fermilab's Tevatron collider and collected by the CDF II detector. In the mode where the top quark decays to a $W$ boson and a bottom quark, we select events in which one $W$ decays leptonically and the other hadronically~(lepton + jets channel) . From a data sample corresponding to 4.3~fb$^{-1}$ of integrated luminosity, we identify 756 candidate events. The top-quark mass and the mass of $W$ boson that decays hadronically are reconstructed for each event and compared with templates of different top-quark widths~($\Gamma_t$) and deviations from nominal jet energy scale~($\Delta_{JES}$) to perform a simultaneous fit for both parameters, where $\Delta_{JES}$ is used for the {\it in situ} calibration of the jet energy scale. By applying a Feldman-Cousins approach, we establish an upper limit at 95$\%$ confidence level~(CL) of $\Gamma_t <$ 7.6 GeV and a two-sided 68$\%$ CL interval of 0.3 GeV $< \Gamma_t <$ 4.4 GeV for a top-quark mass of 172.5 GeV$/c^2$, which are consistant with the standard model prediction. This is the first direct measurement of $\Gamma_t$ to set a lower limit with 68$\%$ CL.