Measurement of W-Boson Polarization in Top-quark Decay in ppbar Collisions at sqrt(s) = 1.96 TeV

TL;DR

This paper measures the polarization states of W bosons from top-quark decays in proton-antiproton collisions, providing results consistent with the Standard Model and improving understanding of top-quark decay dynamics.

Contribution

First measurement of W-boson polarization fractions in top-quark decays at Tevatron energies with model-independent and constrained approaches.

Findings

Measured f_0 = 0.88 ± 0.11 (stat) ± 0.06 (syst)

Measured f_+ = -0.15 ± 0.07 (stat) ± 0.06 (syst)

Results consistent with Standard Model expectations

Abstract

We report measurements of the polarization of W bosons from top-quark decays using 2.7 fb^-1 of ppbar collisions collected by the CDF II detector. Assuming a top-quark mass of 175 GeV/c^2, three measurements are performed. A simultaneous measurement of the fraction of longitudinal (f_0) and right-handed (f_+) W bosons yields the model-independent results f_0 = 0.88 \pm 0.11 (stat) \pm 0.06 (syst) and f_+ = -0.15 \pm 0.07 (stat) \pm 0.06 (syst) with a correlation coefficient of -0.59. A measurement of f_0 (f_+) constraining f_+ (f_0) to its standard model value of 0.0 (0.7) yields f_0 = 0.70 \pm 0.07 (stat) \pm 0.04 (syst) (f_+ = -0.01 \pm 0.02 (stat) \pm 0.05 (syst)). All these results are consistent with standard model expectations.