Measurement of the W boson helicity in top quark decay at D0

TL;DR

This paper measures the fraction of right-handed W bosons in top quark decays using data from the D0 detector, finding results consistent with the Standard Model prediction.

Contribution

First measurement of the W boson helicity fraction in top quark decays at the Tevatron using the D0 detector data.

Findings

Measured f_+ = 0.056 ± 0.080 (stat) ± 0.057 (syst)

Upper limit of f_+ < 0.23 at 95% confidence level

Results are consistent with the Standard Model prediction of near zero

Abstract

We present a measurement of the fraction f_+ of right-handed W bosons produced in top quark decays, based on a candidate sample of ttbar events in the l+jets and dilepton decay channels corresponding to an integrated luminosity of 370 pb^-1 collected by the DO detector at the Fermilab Tevatron ppbar Collider at sqrt{s}=1.96 TeV. We reconstruct the decay angle theta^* for each lepton. By comparing the \cos\theta^* distribution from the data with those for the expected background and signal for various values of f_+, we find $f_+=0.056 +- 0.080 (stat) +- 0.057 (syst)}. (f_+ < 0.23 at 95% C.L.), consistent with the standard model prediction of f_+=3.6 x10^-4.