Can the Minimal Supersymmetric Standard Model with Light Bottom Squark and Light Gluino SurviveZ-Peak Constraints?

In the framework of the minimal supersymmetric model we examine the $Z$-peak constraints on the scenario of one light bottom squark (sbottom) $(\sim 2–5.5\mathrm{GeV})$ and light gluino $(\sim 12–16\mathrm{GeV})$, which has been successfully used to explain the excess of bottom quark production in hadron collisions. Such a scenario is found to be severely constrained by the CERN LEP $Z$-peak observables, especially by $R_b$, due to the large effect of gluino-sbottom loops. To account for the $R_b$ data in this scenario, the other mass eigenstate of sbottom, i.e., the heavier one, must be lighter than 125 (195) GeV at $2\sigma \left(3\sigma \right)$ level, which, however, is disfavored by CERN LEP II experiments.