The search for the top squark ($\widetilde{ t}_{ 1}$) within the kinematic reach of Tevatron Run II is of great contemporary interest. Such a $\widetilde{ t}_{ 1}$ can explain the baryon asymmetry of the universe provided $120 ~GeV/c^{ 2} \leq m_{ \widetilde{ t}_{ 1}} \leq m_t$. Moreover if $\Delta m \equiv m_{ \widetilde{ t}_{ 1}}$ - $m_{ \widetilde\chi_1^0}$ is small, where $\widetilde\chi_1^0$ is the LSP, the dark matter relic density as obtained from the WMAP data may be explained via $\widetilde{ t}_{ 1}$- LSP coannihilation. In this scenario the decay $\widetilde{ t}_{ 1} \to c \widetilde\chi_1^0$ is likely to occur with 100 % branching ratio but for small $\Delta m$ the conventional di-jet + $\not E_T$ signal becomes unobservable. We propose a new search strategy based on the $2j + \not E_T$ signature accompanied by an isolated cluster of energy which arises from a decaying heavy particle with characteristic decay length. Our preliminary simulations with PYTHIA indicate that for $100 ~GeV/c^{ 2} \le m_{ \widetilde{ t}_{ 1}} \le 130 ~GeV/c^{ 2}$ this signal may be observable while somewhat lager $m_{ \widetilde{ t}_{ 1}}$ may still provide hints of new physics.
Categories: hep-ph