QCD-corrected spin analysing power of jets in decays of polarized top quarks

TL;DR

This work extends QCD-corrected analyses of top-quark spin to non-leptonic decays, providing the first full next-to-leading order treatment of jet-based spin analysing powers in t↑ → b d̄ u. By computing virtual and real gluon corrections with infrared-safe jet definitions (E-algorithm and Durham) and evaluating the differential distributions, the authors quantify how QCD effects shift the spin analysing powers of the b-jet, the least energetic light jet, and the thrust axis. The corrections range from modest to sizable (-7.2% to +1.4%), with jet-based analysers generally weaker than their parton-level counterparts, though still offering robust polarization information. These results fill a crucial gap for accurate, polarization-aware NLO analyses of top-quark production and decay at hadron and lepton colliders. They also establish practical benchmarks for experimental extraction of top-quark polarization using jets and thrust as spin analysers.

Abstract

We present results for the differential distributions of jets from non-leptonic decays of polarized top quarks within the Standard Model, including QCD radiative corrections. Our work extends existing results which are only available for semileptonic top quark decays at the parton level. For $t(\uparrow)$ -> b-jet + 2 light jets we compute in particular the QCD-corrected top-spin analysing power of the b-quark jet and the least energetic light jet. The dependence of the results on the choice of the jet recombination scheme is found to be small. In addition we compute the spin analysing power of the thrust axis. Our results constitute a so far missing ingredient to analyse top quark production and subsequent non-leptonic decay at next-to-leading order in alpha_s, keeping the full information on the top quark polarization.