Lecture on a Z' Coupled to Beauty and Truth

Abstract

By extending the standard gauge group to $SU(3)_c \times SU(2)_L \times U(1)_Y \times U(1)_X$ with $X$ charges carried only by the third family we accommodate the LEP measurement of $R_b$ and predict a potentially measurable discrepancy in $A_{FB}^{b}$ in $e^+e^-$ scattering and that $D^0 \bar D^0$ mixing may be near its experimental limit. The uniqueness of our model is that the Z' couplings are generation-dependent and hence explicitly violate the GIM mechanism, but can nevertheless be naturally consistent with FCNC constraints. Direct detection of this Z' is possible but challenging.