Minimal supersymmetry confronts $R_b$, $A^b_{FB}$ and $m_h$

英文摘要：

We study the impact of the measurements of three sets of observables on the parameter space of the constrained minimal supersymmetric Standard Model (cMSSM), its slightly general variant, the non-universal scalar model (NUSM), and some selected benchmark points of the 19-parameter phenomenological MSSM (pMSSM): ($i$) the direct measurement of the Higgs boson mass $m_h \approx 125$ GeV at the CERN Large Hadron Collider (LHC); ($ii$) $Z$ boson decay width in the $b \bar{b}$ channel normalized to its hadronic width ($R_b$), and the forward-backward asymmetry on the $Z$-peak in the same channel $(A_{\rm FB}^b)$; and ($iii$) several $B$-physics observables, along with $(g-2)$ of muon. In addition, there are constraints from non-observation of superparticles from direct searches at the LHC. In view of the recently re-estimated standard model (SM) value of $R_b$ with improved higher order corrections, the measured value of $R_b$ has a 1.2$σ$ discrepancy with its SM value, while the corresponding discrepancy in $A_{\rm FB}^b$ is 2.5$σ$. MSSM contributions from light superpartners improve the agreement of $R_b$ but worsen that of $A_{\rm FB}^b$. We project this ($R_b$-$A_{\rm FB}^b$) tension {\em vis-à-vis} the constraints arising from other observables in the parameter space of cMSSM and NUSM. We also consider a few well-motivated pMSSM benchmark points and show that pMSSM does not fare any better than the SM.