SUSY effects in Rb: Revisited under current experimental constraints

In this note we revisit the SUSY effects in Rb under current experimental constraints including the LHC Higgs data, the B-physics measurements, the dark matter relic density and direct detection limits, as well as the precision electroweak data. We first perform a scan to figure out the currently allowed parameter space and then display the SUSY effects in Rb. We find that although the SUSY parameter space has been severely restrained by current experimental data, both the general MSSM and the natural-SUSY scenario can still alter Rb with a magnitude sizable enough to be observed at future Z-factories (ILC, CEPC, FCC-ee, Super Z-factory) which produce 109-1012 Z-bosons. To be specific, assuming a precise measurement δRb=2.0×10−5 at FCC-ee, we can probe a right-handed stop up to 530 GeV through chargino-stop loops, probe a sbottom to 850 GeV through neutralino-sbottom loops and a charged Higgs to 770 GeV through the Higgs-top quark loops for a large tan⁡β. The full one-loop SUSY correction to Rb can reach 1×10−4 in natural SUSY and 2×10−4 in the general MSSM.