Speaker
Description
We present a jet substructure-based polarimetry framework for boosted heavy neutrino fat jets at the HL-LHC, with the goal of probing the chiral structure of heavy $W'$ interactions. In the boosted regime, a heavy neutrino $N$ produced via $pp \to W' \to \ell N$ and decaying as $N \to \ell jj$ gives rise to a collimated final state. This final state can be reconstructed as a large-radius 3-pronged fat jet containing an embedded lepton. This topology provides a unique opportunity to access polarization information directly from jet substructure.
The central contribution of this work is the construction of three novel polarization-sensitive jet substructure observables namely, $z_{\ell}$, $z_{\theta}$, and $z_{k}$. These variables are physically motivated by the spin-analyzing power of the decay products of $N$ and are designed to encode the underlying chiral structure of the interaction, distinguishing between left-chiral $(V-A)$ and right-chiral $(V+A)$ couplings in a model-independent manner. When combined into a multivariate discriminant using boosted decision trees and evaluated with a $\mathrm{CL}_{s}$-type profile likelihood estimator, these observables achieve a discrimination significance of $1.6\sigma$-$2.8\sigma$ between the two chiral coupling hypotheses at an integrated luminosity of $3~\mathrm{ab}^{-1}$.