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A<sc>bstract</sc> In this work, we present a new technique to measure the longitudinal and transverse polarization fractions of hadronic decays of boostedWbosons. We introduce a new jet substructure observable denoted asp_θ, which is a proxy constructed purely out of subjet energies for the parton level decay polar angle of theWboson in its rest-frame. The distribution of this observable is sensitive to the polarization ofWbosons and can therefore be used to reconstruct theWpolarization in a way that is independent of the production process — assuming Standard Model (SM) rules governing decays. We argue that this proxy variable has lower reconstruction errors as compared to the other proxies that have been used by the experimental collaborations, especially for large boosts of theW-boson. As a test case, we study the efficacy of our technique on vector boson scattering (VBS) processes at the high luminosity Large Hadron Collider. We find that with only SM production channels, measuring the longitudinal polarization fraction is likely to be challenging even with 10 ab⁻¹of data. We suggest further strategies and scenarios that may improve the prospects of measurement of the hadronicWpolarization fraction. 

A bstract We explore the constraints which can be derived on Wilson coefficients in the Standard Model Effective Field Theory from dilepton production, notably including the constraints on operators which do not lead to cross sections growing with energy relative to the Standard Model rate, i.e. shifts. We incorporate essential theory error estimates from higher EFT orders in the analysis in order to provide robust bounds. We find that constraints on four-fermion operator contributions which do grow with energy are not materially weakened by the inclusion of these shifts, and that a constraint on the shifts can also be derived, with a characteristic strength comparable to, and a directionality in parameter space complementary to, those from LEP data. This completes the study of hadronically-quiet dilepton production in the SMEFT, and provides two new constraints which are linearly independent from others arising at the LHC and also rotated in Wilson coefficient space relative to, though not completely independent from, the LEP bounds.