W boson polarization measurement in the ttbar dilepton channel using the CDF II Detector

TL;DR

This paper measures the polarization states of W bosons in top-quark decays using dilepton events at the Tevatron, providing results consistent with the Standard Model.

Contribution

It presents a novel measurement of W boson polarization in dilepton channels, combining with previous results for improved accuracy.

Findings

Measured longitudinal fraction f_0 = 0.71 with uncertainties

Measured right-handed fraction f_+ = -0.07 with uncertainties

Results align with Standard Model predictions

Abstract

We present a measurement of $W$ boson polarization in top-quark decays in $t\bar{t}$ events with decays to dilepton final states using $5.1 {\rm fb^{-1}}$ of integrated luminosity in $p\bar{p}$ collisions collected by the CDF II detector at the Tevatron. A simultaneous measurement of the fractions of longitudinal ($f_0$) and right-handed ($f_+$) $W$ bosons yields the results $f_0 = 0.71 ^{+0.18}_{-0.17} {\rm (stat)} \pm 0.06 {\rm (syst)}$ and $f_+ = -0.07 \pm 0.09 {\rm (stat)} \pm 0.03 {\rm (syst)}$. Combining this measurement with our previous result based on single lepton final states, we obtain $f_0 = 0.84 \pm 0.09 {\rm (stat)} \pm 0.05 {\rm (syst)}$ and $f_{+} = -0.16 \pm 0.05 {\rm (stat)} \pm 0.04 {\rm (syst)}$. The results are consistent with standard model expectation.