Four body decay of the top squark at the upgraded Fermilab Tevatron

We investigate the prospect of a top squark search at the Fermilab Tevatron run-II in MSUGRA motivated as well as unconstrained supersymmetric models, when the lighter top squark turns out to be the next lightest supersymmetric particle (NLSP). In this case, the decay into a four body final state consisting of a b quark, the lightest neutralino, and two light fermions may compete with the much publicized loop-induced two body decay into a charm quark and the lightest neutralino. We systematically study the parameter space in MSUGRA where the lighter top squark turns out to be the NLSP and calculate the branching ratios of the competing channels in both models. Our results show that the four body decay may indeed be the main discovery channel particularly in the low $\mathrm{tan}\ensuremath{\beta}$ scenarios. We discuss the detectability of top squark pairs in the four body decay channel leading to one lepton $(e$ or $\ensuremath{\mu})$ with two or more jets, accompanied by a large amount of missing energy. We also study the corresponding background processes and the kinematic cuts required to suppress them using parton level Monte Carlo simulations. We comment upon, with illustrative examples, the required revision of the existing mass limits of the top squark NLSP assumed to decay solely into the loop-induced two body channel.