Measurement of helicity parameters in top quark decay

Abstract.

It is important to be able to quantitatively assay future measurements of competing observables consistent with the $g_{V-A}$ coupling predictions for $t \rightarrow W^+ b$ decay, so plots of the values of these helicity parameters are given in terms of a “$(V- A)$ + Additional Lorentz Structure”. Three phase-type ambiguities are shown to exist, but measurement of the sign of the large interference between the W longitudinal/transverse amplitudes will resolve two of them. The large $m_b$ effects in both $b_L$ and $b_R$ amplitudes from some couplings demonstrate that it is less model dependent to measure helicity parameters, instead of setting limits on some arbitrary subset of coupling constants.