Top quark polarization as a probe of models with extra gauge bosons

Abstract

New heavy gauge bosons exist in many models of new physics beyond the standard model of particle physics. Discovery of these ${W}^{\ensuremath{'}}$ and ${Z}^{\ensuremath{'}}$ resonances and the establishment of their spins, couplings, and other quantum numbers would shed light on the gauge structure of the new physics. The measurement of the polarization of the SM fermions from the gauge boson decays would decipher the handedness of the coupling of the new states, an important relic of the primordial new physics symmetry. Since the top quark decays promptly, its decay preserves spin information. We show how decays of new gauge bosons into third generation fermions (${W}^{\ensuremath{'}}\ensuremath{\rightarrow}tb$, ${Z}^{\ensuremath{'}}\ensuremath{\rightarrow}t\overline{t}$) can be used to determine the handedness of the couplings of the new states and to discriminate among various new physics models.