Helicity of the W Boson in Lepton+Jets ttbar Events

TL;DR

This paper measures the helicity fractions of W bosons in top-antitop decay events using data from the Fermilab Tevatron, finding results consistent with Standard Model predictions within uncertainties.

Contribution

It introduces a direct probability-based method to determine W boson helicities in ttbar events from collider data.

Findings

Measured longitudinal helicity fraction F_0=0.56±0.31

Results are consistent with the Standard Model prediction of F_0=0.70

Analyzed 125 pb^-1 of data from Fermilab Tevatron Run I

Abstract

We examine properties of ttbar candidates events in lepton+jets final states to establish the helicities of the W bosons in t->W+b decays. Our analysis is based on a direct calculation of a probability that each event corresponds to a ttbar final state, as a function of the helicity of the W boson. We use the 125 events/pb sample of data collected by the DO experiment during Run I of the Fermilab Tevatron collider at sqrt{s}=1.8 TeV, and obtain a longitudinal helicity fraction of F_0=0.56+/-0.31, which is consistent with the prediction of F_0=0.70 from the standard model.