Search for new physics in rare top decays: t(t)over-bar spin correlations and other observables

In this paper we study new-physics contributions to the top-quark decay t -> b (b) over bar bc. We search for ways of detecting such new physics via measurements at the LHC. As top quarks are mainly produced at the LHC in t (t) over bar production via gluon fusion, we analyze the process gg -> t (t) over bar -> (b (b) over barc)((b) over barl (nu) over bar). We find six observables that can be used to reveal the presence of new physics in t -> b (b) over barc. Three are invariant mass-squared distributions involving two of the final-state particles in the top decay, and three are angular correlations between the final-state quarks coming from the t decay and the l(-)coming from the (t) over bar decay. The angular correlations are related to the t (t) over bar spin correlation.