Speaker
Description
In this work, we introduce a novel technique for measuring the longitudinal and transverse polarization fractions of boosted hadronic $W$ boson decays. We propose a jet substructure observable, $p_\theta$, derived from subjet energies, serving as a proxy for the $W$ boson's parton-level decay polar angle in its rest-frame. This observable is sensitive to $W$ boson polarization and offers lower reconstruction errors than existing proxies, especially for highly boosted $W$ bosons. We demonstrate the effectiveness of our method using vector boson scattering processes at the High Luminosity LHC. With 10 ab$^{-1}$ of data, our technique achieves a 20% error in measuring the transverse $W$ polarization fraction. While detecting longitudinal polarization consistent with the Standard Model at the 2-$\sigma$ level remains challenging, our method could identify enhancements in beyond Standard Model scenarios, aiding in unitarity restoration studies.
