Measuring the Polarization of Boosted Hadronic Tops

TL;DR

The paper addresses measuring the polarization of boosted hadronic tops without relying on leptonic decays or full rest-frame reconstruction. It introduces a subjet-based polarimeter, z_K, derived from the hardest subjet in the minimum-kT pair among three subjets inside a top jet, and demonstrates its robustness across multiple MC generators and new-physics scenarios. The method preserves distinct polarization signatures for left- versus right-handed tops after showering and hadronization, making it a practical probe of chiral couplings in top quark production. This approach broadens the experimental reach for top polarization studies and offers a complementary handle on physics beyond the Standard Model at the LHC.

Abstract

We propose a new technique for measuring the polarization of hadronically decaying boosted top quarks. In particular, we apply a subjet-based technique to events where the decay products of the top are clustered within a single jet. The technique requires neither b-tagging nor W-reconstruction, and does not rely on assumptions about either the top production mechanism or the sources of missing energy in the event. We include results for various new physics scenarios made with different Monte Carlo generators to demonstrate the robustness of the technique.