NNLO QCD corrections to the polarized top quark decay $t(\uparrow) \to X_b+W^+$

TL;DR

This paper calculates the NNLO QCD corrections to the decay of a polarized top quark, providing precise predictions for the spin-momentum correlation and asymmetry parameter in this process.

Contribution

It presents the first NNLO QCD correction calculation for the polarized top quark decay, improving theoretical accuracy for top decay observables.

Findings

NNLO correction to the asymmetry parameter is 0.3792±0.0037.

Enhanced precision in the spin-momentum correlation predictions.

Provides a benchmark for future top quark decay studies.

Abstract

We compute the next-to-next-to-leading order (NNLO) QCD corrections to the decay $t(\uparrow) \to X_b +W^+$ of a polarized top quark. The spin-momentum correlation in this quasi two-body decay is described by the polar angle distribution $\mathrm{d}\Gamma/\mathrm{d}\cos\theta_P=\frac{\Gamma}{2}(1+P_t\, \alpha_P\, \cos\theta_P)$ where $P_t$ is the polarization of the top quark and $\alpha_P$ denotes the asymmetry parameter of the decay. For the latter we find $\alpha^{\mathrm{NNLO}}_P=0.3792\pm 0.0037$.