Measurement of W boson Helicity in Top Quark Decay

TL;DR

This paper measures the helicity fractions of W bosons in top quark decays using data from the Fermilab Tevatron, finding results consistent with the Standard Model predictions.

Contribution

First measurement of W boson helicity fractions in top decays using tbar events at the Tevatron with detailed statistical and systematic analysis.

Findings

Measured f_0 = 0.669 ± 0.078 (stat.) ± 0.065 (syst.)

Measured f_+ = 0.023 ± 0.041 (stat.) ± 0.034 (syst.)

Results are consistent with Standard Model expectations.

Abstract

We present a measurement of the helicity of the W boson produced in top quark decays using \ttbar ~decays in the $\ell+$jets and dilepton final states selected from a sample of 5.4 fb$^{-1}$ of collisions recorded using the D0 detector at the Fermilab Tevatron \ppbar\ collider. We measure the fractions of longitudinal and right-handed $W$ bosons to be $f_0 = 0.669 \pm 0.078 \hbox{(stat.)} \pm 0.065 \hbox{(syst.)}$ and $f_+ = 0.023 \pm 0.041 \hbox{(stat.)} \pm 0.034 \hbox{(syst.)}$, respectively. This result is consistent at the 98% level with the standard model. A measurement with $f_0$ fixed to the value from the standard model yields $f_+ = 0.010 \pm 0.022 \hbox{(stat.)} \pm 0.030 \hbox{(syst.).