PHENOMENOLOGY OF LIGHT TOP SQUARKS AT THE FERMILAB TEVATRON

We consider the possibility that one of the supersymmetric partners of the t quark (the t1) is considerably lighter than all the other squarks as well as lighter than the top. We show that t1 will decay into a chargino and a bottom quark if this decay is kinematically accessible; otherwise, it decays via t1 --> c + Z1, where Z1, the lightest neutralino, is also the lightest supersymmetric particle (LSP). We then show that a t1 with a mass just larger than M(Z)/2 could easily have escaped detection at the Fermilab Tevatron. Such a t1 can completely alter the decay patterns of the top quark; if m(t) < M(W) + m(b), the t dominantly decays via t --> t1 + Z1 when this decay is kinematically accessible. This then invalidates any bounds on m(t) obtained from searches for isolated leptons. We show that if the LSP mass is around 10 GeV, it is possible that a top as light as 60 GeV could have escaped detection even via the missing-is-not-an-element-ofE(T) analysis of the Collider Detector at Fermilab Collaboration. Finally, we evaluate the prospects for t1 detection in future Tevatron runs and also examine how signals for a heavy t may be modified if there is a light t1.