Production and decay of scalar top squarkonium bound states

In this paper we discuss possible signatures for the production of scalar ${\tilde{t}}_1{\tilde{t}}_1^{*}$ (top squarkonium) bound states ${\sigma }_{{\tilde{t}}_1}$ at hadron colliders, where ${\tilde{t}}_1$ is the lighter scalar top eigenstate. We first study the decay of ${\sigma }_{{\tilde{t}}_1}$; explicit expressions are given for all potentially important decay modes. If ${\tilde{t}}_1$ has unsuppressed two-body decays, they will always overwhelm the annihilation decays of ${\sigma }_{{\tilde{t}}_1}$. Among the latter, we find that usually either the $\mathrm{gg}$ or $\mathrm{hh}$ final state dominates, depending on the size of the off-diagonal entry of the top squark mass matrix; $h$ is the lighter neutral scalar Higgs boson of the minimal supersymmetric model. If $m_{{\sigma }_{\tilde{t}}}$ happens to be close to the mass of one of the neutral scalar Higgs bosons, $Q\overline{Q}$ final states dominate ($Q=b or t$). $W^{+}{W}^{-}$ and $\mathrm{ZZ}$ final states are subdominant. We argue that ${\sigma }_{{\tilde{t}}_1}\to \gamma \gamma$ decays offer the best signal for top squarkonium production at hadron colliders. The Fermilab Tevatron should be able to close the light top squark window left open by CERN LEP searches, but its mass reach is limited to $m_{{\sigma }_{\tilde{t}}}\le 90$ GeV. In contrast, at the CERN LHC one should ultimately be able to probe the region $m_{{\sigma }_{\tilde{t}}}\le 700$ GeV, if the $\mathrm{hh}$ partial width is not too large. We also comment on the feasibility of searching for ${\sigma }_{{\tilde{t}}_1}$ production at hadron colliders in the $\mathrm{ZZ}$, $Z\gamma$, and ${\tau }^{+}{\tau }^{+}{\tau }^{-}{\tau }^{-}$ final states, and briefly mention ${\sigma }_{{\tilde{t}}_1}$ production at $\gamma \gamma$ colliders.