Measurement of Leptonic Asymmetries and Top Quark Polarization in ttbar Production

TL;DR

This paper reports measurements of leptonic asymmetries and top quark polarization in top-antitop production at the Fermilab Collider, finding results consistent with the Standard Model and providing new insights into top quark properties.

Contribution

The study presents the first measurement of top-quark polarization and combines leptonic asymmetry results from different decay channels at the Tevatron.

Findings

Measured leptonic forward-backward asymmetry A^l_FB = (11.8 +- 3.2)%

Found leptonic asymmetries consistent with Standard Model predictions

Provided the first study of top-quark polarization in this context

Abstract

We present measurements of lepton (l) angular distributions in ttbar -> W+ b W- b -> l+ nu b l- nubar bbar decays produced in ppbar collisions at a center-of-mass energy of sqrt(s)=1.96TeV, where l is an electron or muon. Using data corresponding to an integrated luminosity of 5.4fb^-1, collected with the D0 detector at the Fermilab Collider, we find that the angular distributions of l- relative to anti-protons and l+ relative to protons are in agreement with each other. Combining the two distributions and correcting for detector acceptance we obtain the forward-backward asymmetry A^l_FB = (5.8 +- 5.1(stat) +- 1.3(syst))%, compared to the standard model prediction of A^l_FB (predicted) = (4.7 +- 0.1)%. This result is further combined with the measurement based on the analysis of the l+jets final state to obtain A^l_FB = (11.8 +- 3.2)%. Furthermore, we present a first study of the top-quark polarization.