Four Body Decay of the Stop Squark at the Upgraded Tevatron

We investigate the prospect of stop squark search at Tevatron RUN-II in mSUGRA motivated as well as unconstrained supersymmetric models, when the lighter stop squark turns out to be the next lightest supersymmetric particle (NLSP). In this case the decay into a 4-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 stop 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 tan $\beta$ scenarios. We discuss the detectability of stop squark pairs in the 4-body decay channel leading to one lepton with 2 or more jets accompanied by a large amount of missing energy. We also studied the corresponding background processes and the kinematic cuts required to suppress them using parton level Monte Carlo simulations. We have commented upon with illustrative examples, the required revision of the existing mass limits of the stop NLSP assumed to decay solely into the loop induced 2-body channel in the presence of the competing 4-body decay.