A 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 gluino-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 gluino-LSP. We next investigate limits on a (heavy) gluino-LSP deriving from LEP, LEP2 and RunI Tevatron experimental searches for excess events in the jets plus missing momentum channel and for stable heavily-ionizing charged particles. The range of gluino mass that can be excluded depends upon the path length of the gluino in the detector, the amount of energy it deposits in each hadronic collision, and the probability for the gluino to fragment to a pseudo-stable charged hadron after a given hadronic collision. We explore how the range of excluded gluino mass depends upon these ingredients, concluding that for non-extreme cases the range $3\gev\lsim\mgl\lsim 130-150\gev$ can be excluded at 95% CL based on currently available OPAL and CDF analyses. We find that RunII at the Tevatron can extend the excluded region (or discover the gluino) up to $\mgl\sim 160-180\gev$. For completeness, we also analyze the case where the gluino is the NLSP (as possible in gauge-mediated supersymmetry breaking) decaying via gluino -> g + gravitino. We find that the Tevatron RunI data excludes $\mgl\leq 240$ GeV. Finally, we discuss application of the procedures developed for the heavy gluino-LSP to searches for other stable strongly interacting particles, such as a stable heavy quark.