Heavy gluino as the lightest supersymmetric particle

Abstract

We consider the possibility that the lightest supersymmetric particle is a heavy gluino. After discussing models in which this is the case, we demonstrate that the $\stackrel{\ifmmode \tilde{}\else \~{}\fi{}}{g}\ensuremath{-}\mathrm{LSP}$ could evade cosmological and other constraints by virtue of having a very small relic density. We then consider how neutral and charged hadrons containing a gluino will behave in a detector, demonstrating that there is generally substantial apparent missing momentum associated with a produced $\stackrel{\ifmmode \tilde{}\else \~{}\fi{}}{g}\ensuremath{-}\mathrm{LSP}.$ We next investigate limits on the $\stackrel{\ifmmode \tilde{}\else \~{}\fi{}}{g}\ensuremath{-}\mathrm{LSP}$ deriving from CERN, LEP, LEP2 and run I Fermilab Tevatron experimental searches for excess events in the jets plus missing momentum channel and for stable heavily ionizing charged particles. The range of ${m}_{\stackrel{\ifmmode \tilde{}\else \~{}\fi{}}{g}}$ that can be excluded depends upon the path length of the $\stackrel{\ifmmode \tilde{}\else \~{}\fi{}}{g}$ in the detector, the amount of energy it deposits in each hadronic collision, and the probability for the $\stackrel{\ifmmode \tilde{}\else \~{}\fi{}}{g}$ to fragment to a pseudo-stable charged hadron after a given hadronic collision. We explore how the range of excluded ${m}_{\stackrel{\ifmmode \tilde{}\else \~{}\fi{}}{g}}$ depends upon these ingredients, concluding that for non-extreme cases the range $3\mathrm{GeV}\ensuremath{\lesssim}{m}_{\stackrel{\ifmmode \tilde{}\else \~{}\fi{}}{g}}\ensuremath{\lesssim}130--150\mathrm{GeV}$ can be excluded at 95% C.L. based on currently available OPAL and CDF analyses. We find that run II at the Tevatron can extend the excluded region (or discover the $\stackrel{\ifmmode \tilde{}\else \~{}\fi{}}{g})$ up to ${m}_{\stackrel{\ifmmode \tilde{}\else \~{}\fi{}}{g}}\ensuremath{\sim}160--180\mathrm{GeV}.$ For completeness, we also analyze the case where the $\stackrel{\ifmmode \tilde{}\else \~{}\fi{}}{g}$ is the NLSP (as possible in gauge-mediated supersymmetry breaking) decaying via $\stackrel{\ifmmode \tilde{}\else \~{}\fi{}}{g}\ensuremath{\rightarrow}g+\mathrm{gravitino}.$ We find that the Tevatron run I data exclude ${m}_{\stackrel{\ifmmode \tilde{}\else \~{}\fi{}}{g}}<~240\mathrm{GeV}.$ Finally, we discuss application of the procedures developed for the heavy $\stackrel{\ifmmode \tilde{}\else \~{}\fi{}}{g}\ensuremath{-}\mathrm{LSP}$ to searches for other stable strongly interacting particles, such as a stable heavy quark.