Search for New Physics in Rare Top Decays: $t \bar t$ Spin Correlations and Other Observables

In this paper we study new-physics contributions to the top-quark decay t → bbc. We search for ways of detecting such new physics via measurements at the LHC. As top quarks are mainly pro- duced at the LHC in tt production via gluon fusion, we analyze the process gg → tt → bbcblν � . We find six observables that can be used to reveal the presence of new physics in t → bbc. 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 decay. The angular correlations are related to the tt spin correlation.