General Analysis of Single Top Production and W Helicity in Top Decay

TL;DR

This work addresses how to test electroweak symmetry breaking by probing the tbW vertex in top quark decays with a general effective coupling framework. It combines a non-linear electroweak chiral Lagrangian for the tbW interaction with explicit expressions for W helicity fractions $f_0$, $f_+$, $f_-$ and single-top cross sections $\sigma_t$, $\sigma_s$, mapping them to four couplings $\epsilon_L$, $f_1^R$, $f_2^L$, $f_2^R$. The paper derives concrete formulas and demonstrates, for MSSM and TC2, how deviations in these observables reveal the underlying EWSB dynamics, with the LHC capable of distinguishing the models. It emphasizes that all four observables are required for a complete determination of the tbW vertex and for discriminating between new physics scenarios in the top sector.

Abstract

We provide a framework for the analysis of the W boson helicity in the decay of the top quark that is based on a general effective tbW coupling. Four independent coupling coefficients can be uniquely determined by the fractions of longitudinal and transverse W boson polarizations as well as the single top production rates for the t-channel and the s-channel processes. The knowledge of these coefficients can be used to discriminate models of electroweak symmetry breaking.

Figures (2)

• Figure 1: The coefficients for the s and t channels of single $t'$ production as given by Eqs. (\ref{['sigmat']}) and (\ref{['sigmas']}) at the LHC.
• Figure 2: Possible scenarios and the allowed $f_2^R$ vs $\epsilon_L$ region as given by measurements at the Tevatron and the LHC.