Helicity fractions of W bosons from top quark decays at NNLO in QCD

TL;DR

This paper presents precise calculations of W boson helicity fractions from top quark decays at NNLO in QCD, incorporating finite bottom quark mass and electroweak effects, refining Standard Model predictions.

Contribution

The study provides the first NNLO QCD calculations of top quark decay rates into polarized W bosons with finite bottom quark mass and electroweak corrections.

Findings

Predicted helicity fractions: F_L=0.687(5), F_+=0.0017(1), F_-=0.311(5)

Enhanced precision in Standard Model predictions for top decay observables

Inclusion of electroweak effects and bottom quark mass in NNLO calculations

Abstract

Decay rates of unpolarized top quarks into longitudinally and transversally polarized W bosons are calculated to second order in the strong coupling constant alpha_s. Including the finite bottom quark mass and electroweak effects, the Standard Model predictions for the W boson helicity fractions are F_L=0.687(5), F_+=0.0017(1), and F_-=0.311(5).