A Global Fit of LEP/SLC Data with Light Superpartners

Abstract

We find that re-analyzing the LEP/SLC data with light superpartners and low $α_s(\mz^2)\simeq 0.112$ yields a better fit to the data than the Standard Model, giving a satisfactory description of the $R_b$ measurement, and a better fit to $A_{LR}$. A large body of low energy ($q^2 \ll \mz^2$) data and analyses provide compelling evidence for $α_s(\mz^2)\simeq 0.112$. Global fits to LEP/SLC data in the Standard Model, however, converge on a value of $α_s(\mz^2)\simeq 0.126$. Recently it has become increasingly clear that these should be viewed as incompatible rather than values that can be averaged. We investigate the possibility that new physics is causing the LEP high value. To this end we have conducted a global analysis of LEP/SLC data in the Standard Model and also in the Minimal Supersymmetric Standard Model. Several predictions could confirm (or rule out) the results of this paper: light chargino and stop, top decays into stop and neutralino, large $R_b$, large $A_{LR}$, and a higher $M_W$. We briefly discuss the implications of low $α_s$ for more fundamental high-scale supersymmetric theories.